feat: gcc is too slow on manylinux_s390x, use clang (#1885)

manylinux_s390x uses native gcc (Tier-3) but it's too slow on GHA and we will be reaching job time limit with CPython 3.15.
Move to clang on s390x in order to reduce build time even though it's not supported by CPython.

Author: mayeut

build.sh

@@ -113,7 +113,7 @@ if [ "${MANYLINUX_DISABLE_CLANG_FOR_CPYTHON:-}" == "" ]; then
 		case "${PLATFORM}" in
 			aarch64|x86_64) MANYLINUX_DISABLE_CLANG_FOR_CPYTHON=1;; # gcc is Tier-1, clang is Tier-2
 			armv7l) MANYLINUX_DISABLE_CLANG_FOR_CPYTHON=1;; # gcc is Tier-3, clang not supported at all
-			s390x) MANYLINUX_DISABLE_CLANG_FOR_CPYTHON=1;; # gcc is Tier-3, clang not supported at all
+			# s390x) MANYLINUX_DISABLE_CLANG_FOR_CPYTHON=1;; # gcc is Tier-3, clang not supported at all, gcc is too slow, use clang anyway
 			*) ;;
 		esac
 	fi