Enable testing with _LIBCPP_DEBUG and fix bad assertions in string_view.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@229698 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/test/config.py

@@ -91,6 +91,7 @@ class Configuration(object):
         self.configure_env()
         self.configure_compile_flags()
         self.configure_link_flags()
+        self.configure_debug_mode()
         self.configure_warnings()
         self.configure_sanitizer()
         self.configure_substitutions()
@@ -468,6 +469,15 @@ class Configuration(object):
         else:
             self.lit_config.fatal("unrecognized system: %r" % target_platform)
 
+    def configure_debug_mode(self):
+        debug_level = self.get_lit_conf('debug_level', None)
+        if not debug_level:
+            return
+        if debug_level not in ['0', '1']:
+            self.lit_config.fatal('Invalid value for debug_level "%s".'
+                                  % debug_level)
+        self.cxx.compile_flags += ['-D_LIBCPP_DEBUG=%s' % debug_level]
+
     def configure_warnings(self):
         enable_warnings = self.get_lit_bool('enable_warnings', False)
         if enable_warnings: