Index: lit.cfg
===================================================================
--- lit.cfg
+++ lit.cfg
@@ -291,6 +291,10 @@
                 "inferred use_clang_verify as: %r" % self.use_clang_verify)
 
     def configure_features(self):
+        additional_features = self.get_lit_conf('additional_features').split(",")
+        for f in additional_features:
+            self.config.available_features.add(f)
+
         # Figure out which of the required locales we support
         locales = {
             'Darwin': {
@@ -351,6 +355,12 @@
             self.config.available_features.add(
                 'with_system_lib=%s' % sanitized_triple)
 
+        if 'libcpp-has-no-threads' in self.config.available_features:
+            self.compile_flags += ['-D_LIBCPP_HAS_NO_THREADS']
+
+        if 'no-monotonic-clock' in self.config.available_features:
+            self.compile_flags += ['-D_LIBCPP_HAS_NO_MONOTONIC_CLOCK']
+
     def configure_compile_flags(self):
         # Configure extra compiler flags.
         self.compile_flags += ['-I' + self.src_root + '/include',