build: handle output of localized gcc or clang

build: handle output of localized gcc or clang

Before this commit, we used to scan the output of `$CC -v` for strings like
"gcc version x.y.z".

It was pointed out that this approach fails with localized versions of gcc
because those print (for example) "gcc versión x.y.z".

Use the output of `$CC --version` instead and only look at the first line.