Xcode: add objective C flags to plain C because Xcode requires it.

mesonbuild/backend/xcodebackend.py

@@ -1445,14 +1445,21 @@ class XCodeBackend(backends.Backend):
                 targs = target.get_extra_args(lang)
                 args = warn_args + std_args + pargs + gargs + targs
                 if args:
-                    langname = LANGNAMEMAP[lang]
                     lang_cargs = cargs
                     if compiler and target.implicit_include_directories:
                         # It is unclear what is the cwd when xcode runs. -I. does not seem to
                         # add the root build dir to the search path. So add an absolute path instead.
                         # This may break reproducible builds, in which case patches are welcome.
                         lang_cargs += self.get_custom_target_dir_include_args(target, compiler, absolute_path=True)
-                    langargs[langname] = args
+                    # Xcode can not handle separate compilation flags for C and ObjectiveC. They are both
+                    # put in OTHER_CFLAGS.
+                    if lang == 'objc':
+                        lang = 'c'
+                    langname = LANGNAMEMAP[lang]
+                    if langname in langargs:
+                        langargs[langname] += args
+                    else:
+                        langargs[langname] = args
                     langargs[langname] += lang_cargs
             symroot = os.path.join(self.environment.get_build_dir(), target.subdir)
             bt_dict = PbxDict()

run_tests.py

@@ -225,9 +225,7 @@ def get_backend_commands(backend: Backend, debug: bool = False) -> \
         test_cmd = cmd + ['RUN_TESTS.vcxproj']
     elif backend is Backend.xcode:
         cmd = ['xcodebuild']
-        # In Xcode9 new build system's clean command fails when using a custom build directory.
-        # Maybe use it when CI uses Xcode10 we can remove '-UseNewBuildSystem=FALSE'
-        clean_cmd = cmd + ['-alltargets', 'clean', '-UseNewBuildSystem=FALSE']
+        clean_cmd = cmd + ['-alltargets', 'clean']
         test_cmd = cmd + ['-target', 'RUN_TESTS']
     elif backend is Backend.ninja:
         global NINJA_CMD