Record C compile features flags for MinGW Clang on Windows
This was done for C++ by commit v3.5.0-rc1~69^2 (Record compile features
for MinGW Clang on Windows, 2016-01-11). Make the same change for C.
The `UNIX` condition on Clang C compiler features was already dropped by
refactoring in commit v3.9.0-rc1~17^2~4 (Compilers: Port to use default
cmake_record_lang_compile_features macros, 2017-05-10).
Our documentation already claims support for this combination. This
was simply an oversight when support was added for MinGW Clang C++.
Issue: #15897
Issue: #15943
1 file changed
