Squashed '3rdparty/github/cmake-utils/' changes from 7780542..18d43f2
Squashed '3rdparty/github/cmake-utils/' changes from 7780542..18d43f2

18d43f2 cmake/MyPackageCheckCommonFeatures.cmake: Check also flatten attribute with clang
83bf596 cmake/MyPackageCheckCommonFeatures.cmake: Test function attributes only if compiler support the -Werror compilation flag

git-subtree-dir: 3rdparty/github/cmake-utils
git-subtree-split: 18d43f2d3a7659db8221651d44fc484408f169c1

jddurand/c-tconv,jddurand/c-tconv,jddurand/c-tconv,jddurand/c-tconv