- 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