ipfs: add options to disable

- CPPFLAGS: `-DCURL_DISABLE_IPFS`
- configure: `--disable-ipfs`
- cmake: `-DCURL_DISABLE_IPFS=ON`

Fixes #14824
Closes #14827

src: fix potential macro confusion in cmake unity builds

Sources used `lib/curlx.h` with both `ENABLE_CURLX_PRINTF` set and unset
before including it.

In a cmake "unity" batch w

src: fix potential macro confusion in cmake unity builds

Sources used `lib/curlx.h` with both `ENABLE_CURLX_PRINTF` set and unset
before including it.

In a cmake "unity" batch where the first included source had it unset,
the next sources did not get the macros requested with
`ENABLE_CURLX_PRINTF` because `lib/curl.x` had already been included
without them.

Fix it by by making the macros enabled permanently and globally for
internal sources, and dropping `ENABLE_CURLX_PRINTF`.

This came up while testing unity builds with smaller batches. The full,
default unity build where all `src` is bundled up in a single unit, was
not affected.

Fixes:
```
$ cmake -B build -DCMAKE_UNITY_BUILD=ON -DCMAKE_UNITY_BUILD_BATCH_SIZE=15
$ make -C build
...
curl/src/tool_getparam.c: In function ‘getparameter’:
curl/src/tool_getparam.c:2409:11: error: implicit declaration of function ‘msnprintf’; did you mean ‘vsnprintf’? [-Wimplicit-function-declaration]
2409 | msnprintf(buffer, sizeof(buffer), "%" CURL_FORMAT_CURL_OFF_T "-",
| ^~~~~~~~~
| vsnprintf
curl/src/tool_getparam.c:2409:11: warning: nested extern declaration of ‘msnprintf’ [-Wnested-externs]
[...]
```

Reported-by: Daniel Stenberg
Bug: https://github.com/curl/curl/pull/14626#issuecomment-2301663491

Closes #14632

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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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tool: follow-up getenv fix

Remove a double free. Change the IPFS env use to a plain getenv() simply
because coverity gets confused.

Follow-up to 9126b141c9398fe
Closes #13241

curl: use curl_getenv instead of the curlx_ version

The curlx one was once introduced when we still considered dropping the
libcurl function at some point. To reduce confusion and to mak

curl: use curl_getenv instead of the curlx_ version

The curlx one was once introduced when we still considered dropping the
libcurl function at some point. To reduce confusion and to make it
easier to understand when curl_free() should be used, use the actual
libcurl function call directly instead.

Closes #13230

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build: enable missing OpenSSF-recommended warnings, with fixes

https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html
as of 2023-11-29 [1]

build: enable missing OpenSSF-recommended warnings, with fixes

https://best.openssf.org/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C++.html
as of 2023-11-29 [1].

Enable new recommended warnings (except `-Wsign-conversion`):

- enable `-Wformat=2` for clang (in both cmake and autotools).
- add `CURL_PRINTF()` internal attribute and mark functions accepting
printf arguments with it. This is a copy of existing
`CURL_TEMP_PRINTF()` but using `__printf__` to make it compatible
with redefinting the `printf` symbol:
https://gcc.gnu.org/onlinedocs/gcc-3.0.4/gcc_5.html#SEC94
- fix `CURL_PRINTF()` and existing `CURL_TEMP_PRINTF()` for
mingw-w64 and enable it on this platform.
- enable `-Wimplicit-fallthrough`.
- enable `-Wtrampolines`.
- add `-Wsign-conversion` commented with a FIXME.
- cmake: enable `-pedantic-errors` the way we do it with autotools.
Follow-up to d5c0351055d5709da8f3e16c91348092fdb481aa #2747
- lib/curl_trc.h: use `CURL_FORMAT()`, this also fixes it to enable format
checks. Previously it was always disabled due to the internal `printf`
macro.

Fix them:

- fix bug where an `set_ipv6_v6only()` call was missed in builds with
`--disable-verbose` / `CURL_DISABLE_VERBOSE_STRINGS=ON`.
- add internal `FALLTHROUGH()` macro.
- replace obsolete fall-through comments with `FALLTHROUGH()`.
- fix fallthrough markups: Delete redundant ones (showing up as
warnings in most cases). Add missing ones. Fix indentation.
- silence `-Wformat-nonliteral` warnings with llvm/clang.
- fix one `-Wformat-nonliteral` warning.
- fix new `-Wformat` and `-Wformat-security` warnings.
- fix `CURL_FORMAT_SOCKET_T` value for mingw-w64. Also move its
definition to `lib/curl_setup.h` allowing use in `tests/server`.
- lib: fix two wrongly passed string arguments in log outputs.
Co-authored-by: Jay Satiro
- fix new `-Wformat` warnings on mingw-w64.

[1] https://github.com/ossf/wg-best-practices-os-developers/blob/56c0fde3895bfc55c8a973ef49a2572c507b2ae1/docs/Compiler-Hardening-Guides/Compiler-Options-Hardening-Guide-for-C-and-C%2B%2B.md

Closes #12489

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IPFS: bugfixes

- Fixed endianness bug in gateway file parsing
- Use IPFS_PATH in tests where IPFS_DATA was used
- Fixed typos from traling -> trailing
- Fixed broken link in IPFS

IPFS: bugfixes

- Fixed endianness bug in gateway file parsing
- Use IPFS_PATH in tests where IPFS_DATA was used
- Fixed typos from traling -> trailing
- Fixed broken link in IPFS.md

Follow-up to 859e88f6533f9e

Reported-by: Michael Kaufmann
Bug: https://github.com/curl/curl/pull/12152#issuecomment-1798214137
Closes #12305

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curl: move IPFS code into src/tool_ipfs.[ch]

- convert ensure_trailing into ensure_trailing_slash
- strdup the URL string to own it proper
- use shorter variable names
- combine

curl: move IPFS code into src/tool_ipfs.[ch]

- convert ensure_trailing into ensure_trailing_slash
- strdup the URL string to own it proper
- use shorter variable names
- combine some expressions
- simplify error handling in ipfs_gateway()
- add MAX_GATEWAY_URL_LEN + proper bailout if maximum is reached
- ipfs-gateway.d polish and simplification
- shorten ipfs error message + make them "synthetic"

Closes #12281

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