Scons: run `clang -Wall -fsyntax-only` in clang-analyze

The `clang -fsyntax-only` will give us additional warning messages in
the console.

tools/building.py

@@ -113,8 +113,11 @@ def PrepareBuilding(env, root_directory, has_libcpu=False, remove_components = [
                 AS   = 'true',)
         env["ENV"].update(x for x in os.environ.items() if x[0].startswith("CCC_"))
         # only check, don't compile. ccc-analyzer use CCC_CC as the CC.
-        env['ENV']['CCC_CC']  = 'true'
-        env['ENV']['CCC_CXX'] = 'true'
+        # fsyntax-only will give us some additional warning messages
+        env['ENV']['CCC_CC']  = 'clang'
+        env.Append(CFLAGS=['-fsyntax-only', '-Wall', '-Wno-invalid-source-encoding'])
+        env['ENV']['CCC_CXX'] = 'clang++'
+        env.Append(CXXFLAGS=['-fsyntax-only', '-Wall', '-Wno-invalid-source-encoding'])
         # remove the POST_ACTION as it will cause meaningless errors(file not
         # found or something like that).
         rtconfig.POST_ACTION = ''