configure: Use a hopefully more robust way to fix AX_CHECK_COMPILE_FLAG

The check for -Wno-extra-semi-stmt failed on Linux with clang++-7.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

configure.ac

@@ -112,12 +112,11 @@ case "${host_os}" in
 esac
 
 WERROR=-Werror
-# The test code used by AX_CHECK_COMPILE_FLAG uses an empty statement.
-# clang++-8 can emit a warning for that which must be disabled.
-AX_CHECK_COMPILE_FLAG([-Wno-extra-semi-stmt], [WERROR="$WERROR -Wno-extra-semi-stmt"])
-# The test code used by AX_CHECK_COMPILE_FLAG uses macros which are unused.
-# That must not break the check, so disable a related warning if necessary.
-AX_CHECK_COMPILE_FLAG([-Wno-unused-macros], [WERROR="$WERROR -Wno-unused-macros"])
+# The test code used by AX_CHECK_COMPILE_FLAG uses an empty statement
+# and unused macros which must not raise a compiler error, but it must
+# be an error if flags like -avx are ignored on ARM and other
+# architectures because they are unsupported.
+AX_CHECK_COMPILE_FLAG([-Werror=unused-command-line-argument], [WERROR=-Werror=unused-command-line-argument])
 
 ## Checks for supported compiler options.