cmake: more small tidy-ups and fixes

- tidy up two `MATCHES` expression by avoiding macros expansion and
adding quotes. Then convert then to `STREQUAL` to match other places
in t

cmake: more small tidy-ups and fixes

- tidy up two `MATCHES` expression by avoiding macros expansion and
adding quotes. Then convert then to `STREQUAL` to match other places
in the code doing the same checks.

- fix setting `_ALL_SOURCE` for AIX to match what autotools does.

- delete stray `_ALL_SOURCE` reference from `lib/config_riscos.h`

- simplify/fix two `STREQUAL ""` checks.
The one in the `openssl_check_symbol_exists()` macro succeeded
regardless of the value. The other could return TRUE when
`CMAKE_OSX_SYSROOT` was undefined.

- delete code for CMake versions (<3.7) we no longer support.

- prefer `LIST(APPEND ...)` to extend `CURL_LIBS`.

- use `CURL_LIBS` to add the `network` lib for Haiku.
Before this patch it was done via raw C flags. I could not test this.

- move `_WIN32_WINNT`-related code next to each other.
It also moves detection to the top, allowing more code to use
the result.

- merge two `WIN32` blocks.

- rename internal variables to underscore + lowercase.

- unwrap a line, indent, whitespace.

Closes #14450

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cmake: tidy-ups

- tidy-up comments.
- use lowercase, underscore prefixed names for internal variables.
- use `IN LISTS` and `IN ITEMS` in `foreach()` loops.
- rename variable nam

cmake: tidy-ups

- tidy-up comments.
- use lowercase, underscore prefixed names for internal variables.
- use `IN LISTS` and `IN ITEMS` in `foreach()` loops.
- rename variable name `OUTPUT` to a more distinctive one.
- tidy-up `STREQUAL` syntax.
- delete commented code.
- indent/whitespace.

Closes #14197

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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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copyright: make repository REUSE compliant

Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the

copyright: make repository REUSE compliant

Add licensing and copyright information for all files in this repository. This
either happens in the file itself as a comment header or in the file
`.reuse/dep5`.

This commit also adds a Github workflow to check pull requests and adapts
copyright.pl to the changes.

Closes #8869

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curl.se: new home

Closes #6172

copyright: fix out-of-date copyright ranges and missing headers

Reported by the new script 'scripts/copyright.pl'. The script has a
regex whitelist for the files that don't need copyrigh

copyright: fix out-of-date copyright ranges and missing headers

Reported by the new script 'scripts/copyright.pl'. The script has a
regex whitelist for the files that don't need copyright headers.

Removed three (mostly usesless) README files from docs/

Closes #5141

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CMake: Update scripts to use consistent style

Closes #2727
Reviewed-by: Sergei Nikulov

cmake: move cmake_uninstall.cmake to CMake/

Closes #1756