[libc++] Only add dylib-related features when using the system's libc++

Otherwise, when testing trunk libc++ on an older system, lit will think
that the dylib features are disabled. Ideally, we'd have a notion of
running the tests with/without a deployment target (or, equivalently,
a deployment target representing trunk where everything is as recent
as can be). Since we always have a deployment target right now (which
defaults to the current system), we only enable those features when
we're going to also be testing with the system libc++.

llvm-svn: 353319

Author: ldionne

libcxx/utils/libcxx/test/config.py

@@ -1145,7 +1145,7 @@ def configure_deployment(self):
 
         # Throwing bad_optional_access, bad_variant_access and bad_any_cast is
         # supported starting in macosx10.14.
-        if name == 'macosx' and version in ('10.%s' % v for v in range(7, 14)):
+        if self.get_lit_conf('use_system_cxx_lib') and name == 'macosx' and version in ('10.%s' % v for v in range(7, 14)):
             self.config.available_features.add('dylib-has-no-bad_optional_access')
             self.lit_config.note("throwing bad_optional_access is not supported by the deployment target")