- use the same pattern across all Find modules:
- verify if the version header exists before reading it.
- use a single regex per lookup.
- sync regexes between Find modules.
- use generic temporary variable names.
- improve readability.
- make it simpler to transition to new CMake syntax in the future:
```cmake
file(STRINGS "${CARES_INCLUDE_DIR}/ares_version.h" _version_str REGEX "<...>")
unset(_version_str)
set(CARES_VERSION "${CMAKE_MATCH_1}")
```
Ref: https://cmake.org/cmake/help/latest/policy/CMP0159.html#policy:CMP0159
- fix zstd version detection to be CMake 3.7 compatible.
Required 3.9 before this patch, for the `CMAKE_MATCH_<n>` feature.
Follow-up to c5d506e9bb#12200
Follow-up to 4e2f3641f8#14548Closes#14572
432f2fd9ac