VERSION comparison requires semver-compliant version strings, but
obs-deps versions are based on dates, which are not compliant. Fix
version strings to semver variants before comparison.
As there will be multiple directories containing obs-deps (non-Qt and
Qt variants), the search needs to continue after a first failed attempt
and not abort it entirely.
- Sets CMAKE_C_STANDARD to 17
- Disables C extensions (e.g. gnu17) to force ISO C on macOS/Windows
- Fixes language properties in cmake 3.0 not being set correctly
- Sets Xcode attributes to c17