[libcxx] Add support for LLVM_USE_SANITIZER=Undefined

LLVM_USE_SANITIZER=Undefined support was added to the LLVM CMake configuration.
Update libc++'s handling of LLVM_USE_SANITIZER to support this as well.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@219987 91177308-0d34-0410-b5e6-96231b3b80d8

test/lit.cfg

@@ -434,6 +434,11 @@ class Configuration(object):
                 if san == 'MemoryWithOrigins':
                     self.compile_flags += ['-fsanitize-memory-track-origins']
                 self.config.available_features.add('msan')
+            elif san == 'Undefined':
+                self.compile_flags += ['-fsanitize=undefined',
+                                       '-fno-sanitize=vptr,function',
+                                       '-fno-sanitize-recover']
+                self.config.available_features.add('ubsan')
             else:
                 self.lit_config.fatal('unsupported value for '
                                       'libcxx_use_san: {0}'.format(san))