compilers: Fix builtin checks with clang on Linux

Our "43 has function" test should also work with clang and icc on Linux,
so enable them. Also detect builtins with __has_builtin if available,
which is much faster on clang.

There is a feature request for the same with GCC too:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66970

mesonbuild/compilers.py

@@ -1057,7 +1057,16 @@ int main(int argc, char **argv) {
         # posix_memalign in the headers to point to that builtin which results
         # in an invalid detection.
         if '#include' not in prefix:
-            code = 'int main() {{ {0}; }}'
+            code = '''
+            int main() {{
+            #ifdef __has_builtin
+                #if !__has_builtin({0})
+                    #error "built-in {0} not found"
+                #endif
+            #else
+                {0};
+            #endif
+            }}'''
             return self.links(code.format('__builtin_' + funcname), env,
                               extra_args, dependencies)
         else:

test cases/common/43 has function/meson.build

@@ -31,12 +31,16 @@ foreach cc : compilers
     error('Found non-existent function "hfkerhisadf".')
   endif
 
+  if cc.has_function('hfkerhisadf', args : unit_test_args)
+    error('Found non-existent function "hfkerhisadf".')
+  endif
+
   # With glibc on Linux lchmod is a stub that will always return an error,
   # we want to detect that and declare that the function is not available.
   # We can't check for the C library used here of course, but if it's not
   # implemented in glibc it's probably not implemented in any other 'slimmer'
   # C library variants either, so the check should be safe either way hopefully.
-  if host_system == 'linux' and cc.get_id() == 'gcc'
+  if host_system == 'linux'
     assert (cc.has_function('poll', prefix : '#include <poll.h>',
                             args : unit_test_args),
             'couldn\'t detect "poll" when defined by a header')