Fix a few OSX "features".

mesonbuild/compilers/compilers.py

@@ -1006,7 +1006,7 @@ class ClangCompiler:
 
     def has_multi_arguments(self, args, env):
         return super().has_multi_arguments(
-            ['-Werror=unknown-warning-option'] + args,
+            ['-Werror=unknown-warning-option', '-Werror=unused-command-line-argument'] + args,
             env)
 
     def has_function(self, funcname, prefix, env, extra_args=None, dependencies=None):

test cases/common/139 simd/simd_ssse3.c

@@ -1,12 +1,17 @@
 #include<simdconfig.h>
 #include<simdfuncs.h>
 
+#include<emmintrin.h>
 #include<tmmintrin.h>
 #include<cpuid.h>
 #include<stdint.h>
 
 int ssse3_available() {
+#ifdef __APPLE__
+    return 1;
+#else
     return __builtin_cpu_supports("ssse3");
+#endif
 }
 
 void increment_ssse3(float arr[4]) {