configure: fix WinIDN builds targeting old Windows

1. GHA/windows: enable WinIDN in Linux cross-builds.
(to reveal the issue in CI.)

2. fix compiler warning when building wit

configure: fix WinIDN builds targeting old Windows

1. GHA/windows: enable WinIDN in Linux cross-builds.
(to reveal the issue in CI.)

2. fix compiler warning when building with mingw-w64 supporting
WinIDN, while targeting pre-Vista Windows, with a `WINVER` set to
target Vista or newer. (Such was Ubuntu's mingw-w64 with the
classic-mingw-specific trick in point 3 of this PR.)
```
../../lib/idn.c:154:23: error: redundant redeclaration of ‘IdnToAscii’ [-Werror=redundant-decls]
154 | WINBASEAPI int WINAPI IdnToAscii(DWORD dwFlags,
| ^~~~~~~~~~
In file included from /usr/share/mingw-w64/include/windows.h:73,
from /usr/share/mingw-w64/include/winsock2.h:23,
from ../../lib/setup-win32.h:91,
from ../../lib/curl_setup.h:308,
from ../../lib/idn.c:29:
/usr/share/mingw-w64/include/winnls.h:1075:30: note: previous declaration of ‘IdnToAscii’ was here
1075 | WINNORMALIZEAPI int WINAPI IdnToAscii (DWORD dwFlags, LPCWSTR lpUnicodeCharStr, int cchUnicodeChar, LPWSTR lpASCIICharStr, int cchASCIIChar);
| ^~~~~~~~~~
[...same for IdnToUnicode...]
```
Ref: https://github.com/curl/curl/actions/runs/10542832783/job/29210098553#step:7:89

3. drop `WINVER` override for classic-mingw. curl no longer supports
building with classic-mingw.
Reverts 37f1c21cb9c809ec870803fc40e1ed2afd9534ac #7581

4. sync `if IdnToUnicode can be linked` detection snippet with the live
code in `lib/idn.c`. It fixes detection for the scenario in point 2.

5. delete unused `WINIDN_DIR` variable.

Bug: https://github.com/curl/curl/pull/12606#issuecomment-1885381038
Previous abandoned attempt: #12684
Reviewed-by: Jay Satiro
Closes #14680

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idn: more strictly check AppleIDN errors

UIDNA API returns two error values but we were only checking one.
Checking both better aligns the behaviour with that of libidn2.

Closes

idn: more strictly check AppleIDN errors

UIDNA API returns two error values but we were only checking one.
Checking both better aligns the behaviour with that of libidn2.

Closes #14431

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idn: support non-UTF-8 input under AppleIDN

This aligns the behaviour with libidn2 and the curl documentation.

Closes #14431

idn: make macidn fail before trying conversion if name too long

- double the max name length to 512 bytes

Closes #14215

idn: tweak buffer use when converting with macidn

Closes #14215

IDN: fix ß with AppleIDN

Add flags UIDNA_NONTRANSITIONAL_TO_ASCII and
UIDNA_NONTRANSITIONAL_TO_UNICODE to encode ß correctly.

It fixes test 165.

Reported-by: Viktor Sza

IDN: fix ß with AppleIDN

Add flags UIDNA_NONTRANSITIONAL_TO_ASCII and
UIDNA_NONTRANSITIONAL_TO_UNICODE to encode ß correctly.

It fixes test 165.

Reported-by: Viktor Szakats
Bug: #14176
Closes #14179

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code: language cleanup in comments

Based on the standards and guidelines we use for our documentation.

- expand contractions (they're => they are etc)
- host name = > hostname

code: language cleanup in comments

Based on the standards and guidelines we use for our documentation.

- expand contractions (they're => they are etc)
- host name = > hostname
- file name => filename
- user name = username
- man page => manpage
- run-time => runtime
- set-up => setup
- back-end => backend
- a HTTP => an HTTP
- Two spaces after a period => one space after period

Closes #14073

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idn: add native AppleIDN (icucore) support for macOS/iOS

I implemented the IDN functions for macOS and iOS using Unicode
libraries coming with macOS and iOS.

Builds and runs her

idn: add native AppleIDN (icucore) support for macOS/iOS

I implemented the IDN functions for macOS and iOS using Unicode
libraries coming with macOS and iOS.

Builds and runs here on macOS 14.2.1. Also verified to load and
run on older macOS version 10.13.

Build requires macOS SDK 13 or equivalent.

Set `-DUSE_APPLE_IDN=ON` CMake option to enable it.
With autotools and other build tools, set these manual options:
```
CPPFLAGS=-DUSE_APPLE_IDN
LIBS=-licucore
```

Completes TODO 1.6.

TODO: add autotools option and feature-detection.

Refs: #5330 #5371
Co-authored-by: Viktor Szakats
Closes #13246

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idn: make Curl_idnconvert_hostname() use Curl_idn_decode()

In the name of less code duplication

Closes #13236

windows: use built-in `_WIN32` macro to detect Windows

Windows compilers define `_WIN32` automatically. Windows SDK headers
or build env defines `WIN32`, or we have to take care of it. T

windows: use built-in `_WIN32` macro to detect Windows

Windows compilers define `_WIN32` automatically. Windows SDK headers
or build env defines `WIN32`, or we have to take care of it. The
agreement seems to be that `_WIN32` is the preferred practice here.
Make the source code rely on that to detect we're building for Windows.

Public `curl.h` was using `WIN32`, `__WIN32__` and `CURL_WIN32` for
Windows detection, next to the official `_WIN32`. After this patch it
only uses `_WIN32` for this. Also, make it stop defining `CURL_WIN32`.

There is a slight chance these break compatibility with Windows
compilers that fail to define `_WIN32`. I'm not aware of any obsolete
or modern compiler affected, but in case there is one, one possible
solution is to define this macro manually.

grepping for `WIN32` remains useful to discover Windows-specific code.

Also:

- extend `checksrc` to ensure we're not using `WIN32` anymore.

- apply minor formatting here and there.

- delete unnecessary checks for `!MSDOS` when `_WIN32` is present.

Co-authored-by: Jay Satiro
Reviewed-by: Daniel Stenberg

Closes #12376

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idn: fix WinIDN null ptr deref on bad host

- Return CURLE_URL_MALFORMAT if IDN hostname cannot be converted from
UTF-8 to UTF-16.

Prior to this change a failed conversion erro

idn: fix WinIDN null ptr deref on bad host

- Return CURLE_URL_MALFORMAT if IDN hostname cannot be converted from
UTF-8 to UTF-16.

Prior to this change a failed conversion erroneously returned CURLE_OK
which meant 'decoded' pointer (what would normally point to the
punycode) would not be written to, remain NULL and be dereferenced
causing an access violation.

Closes https://github.com/curl/curl/pull/11983

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idn: if idn2_check_version returns NULL, return error

... this avoids a NULL dereference for this unusual case.

Reported-by: s0urc3_ on hackerone
Closes #11898

urlapi: return CURLUE_BAD_HOSTNAME if puny2idn encoding fails

And document it. Only return out of memory when it actually is a memory
problem.

Pointed-out-by: Jacob Mealey
C

urlapi: return CURLUE_BAD_HOSTNAME if puny2idn encoding fails

And document it. Only return out of memory when it actually is a memory
problem.

Pointed-out-by: Jacob Mealey
Closes #11674

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urlapi: CURLU_PUNY2IDN - convert from punycode to IDN name

Asssisted-by: Jay Satiro
Closes #11655

idn: return error if the conversion ends up with a blank host

Some IDN sequences are converted into "" (nothing), which can make this
function end up with a zero length host name and we

idn: return error if the conversion ends up with a blank host

Some IDN sequences are converted into "" (nothing), which can make this
function end up with a zero length host name and we cannot consider that
a valid host to continue with.

Reported-by: Maciej Domanski
Closes #10617

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copyright: update all copyright lines and remove year ranges

- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- save

copyright: update all copyright lines and remove year ranges

- they are mostly pointless in all major jurisdictions
- many big corporations and projects already don't use them
- saves us from pointless churn
- git keeps history for us
- the year range is kept in COPYING

checksrc is updated to allow non-year using copyright statements

Closes #10205

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urlapi: add CURLU_PUNYCODE

Allows curl_url_get() get the punycode version of host names for the
host name and URL parts.

Extend test 1560 to verify.

Closes #10109

idn: rename the files to idn.[ch] and hold all IDN functions

Closes #10094