Makes building tests noticeably faster. Apply changes/fixes/workarounds to make Unity work: - rename test variables to avoid collisions or shadowing each other when combined into single units. - add workaround to avoid applying `lib/memdebug.h` overrides to system headers declaring/defining `getaddrinfo()`/`freeaddrinfo()` for `tests/server/resolve.c`. This replaces a previous workaround that worked for that specific source. - rename test macro `CTRL` clashing with Cygwin `sys/ioctl.h`. - add include guard to `test.h`. Also: - exclude `tests/http/clients` which are all single-source. (like `docs/examples`.) Build time improvements for tests: - AppVeyor CI: - MSVC 2008, 2010: 1 minute faster (4m8s -> 2m56s, 3m19s -> 2m24s) - MSVC 2022 arm64: 3.5 minutes faster (10m18s -> 6m48s) before: https://ci.appveyor.com/project/curlorg/curl/builds/50522785 after: https://ci.appveyor.com/project/curlorg/curl/builds/50522942 - GHA: - Cygwin: 1.5 minutes faster (3m13s -> 1m43s) before: https://github.com/curl/curl/actions/runs/10681535327/job/29605384398 after: https://github.com/curl/curl/actions/runs/10680818726/job/29603130637 - Windows: before: https://github.com/curl/curl/actions/runs/10680818713 after: https://github.com/curl/curl/actions/runs/10683850187 - MSYS2, mingw-w64: 1 minute faster - MSVC: 30 seconds faster (3m17s -> 2m48s) - macOS: double speed (39s -> 18s) before: https://github.com/curl/curl/actions/runs/10680818753/job/29603133447 after: https://github.com/curl/curl/actions/runs/10683850174/job/29612914515 - Linux: almost double speed (30/31s -> 18s) before: https://github.com/curl/curl/actions/runs/10681535311/job/29605387156 after: https://github.com/curl/curl/actions/runs/10680818721/job/29603133976 - non-native: no obvious effect. before: https://github.com/curl/curl/actions/runs/10680818722 after: https://github.com/curl/curl/actions/runs/10683850187 - Old Linux: Unity mode not supported by old CMake, no effect. Closes #14765