[utils] Add libc++ and libc++abi config to llvm-lit

[smeenai]

Summary

This allows us to use bin/llvm-lit to run individual libc++ and
libc++abi tests without having to explicitly specify the site config
paths, similar to other projects.

[EricWF]

This LGTM.

utils/llvm-lit/llvm-lit.in

if os.path.exists(lld_obj_root):
     builtin_parameters['lld_site_config'] = \
         os.path.join(lld_obj_root, 'test', 'lit.site.cfg')
 
 compilerrt_obj_root = os.path.join(llvm_obj_root, 'projects', 'compiler-rt')
 if os.path.exists(compilerrt_obj_root):
     builtin_parameters['compilerrt_site_basedir'] = \
             os.path.join(compilerrt_obj_root, 'test')
 
+libcxx_obj_root = os.path.join(llvm_obj_root, 'projects', 'libcxx')
+if os.path.exists(libcxx_obj_root):
+    builtin_parameters['libcxx_site_config'] = \
+        os.path.join(libcxx_obj_root, 'test', 'lit.site.cfg')
+
+libcxxabi_obj_root = os.path.join(llvm_obj_root, 'projects', 'libcxxabi')
+if os.path.exists(libcxxabi_obj_root):
+    builtin_parameters['libcxxabi_site_config'] = \
+        os.path.join(libcxxabi_obj_root, 'test', 'lit.site.cfg')
+
 if __name__=='__main__':
     from lit.main import main
     main(builtin_parameters)