Only add -Wno-clobbered flag when the compiler recognizes it

Author: Girgias

Zend/Zend.m4

@@ -222,6 +222,9 @@ else
 fi
 
 test -n "$GCC" && CFLAGS="$CFLAGS -Wall -Wno-strict-aliasing -Wextra -Wno-implicit-fallthrough -Wno-unused-parameter -Wno-sign-compare"
+dnl Check if compiler supports -Wn-clobbered (only GCC)
+AX_CHECK_COMPILE_FLAG([-Wno-clobbered], CFLAGS="$CFLAGS -Wno-clobbered", , [-Werror])
+
 test -n "$DEBUG_CFLAGS" && CFLAGS="$CFLAGS $DEBUG_CFLAGS"
 
 if test "$ZEND_ZTS" = "yes"; then