Add -ldl to libc++ tests when sanitizers are used.

Clang 3.6 no longer links the sanitizer runtime library dependancies when
-nodefaultlibs is used. This patch manually links in a missing dependancy.

llvm-svn: 220463

libcxx/test/lit.cfg

@@ -431,6 +431,8 @@ class Configuration(object):
         san = self.get_lit_conf('llvm_use_sanitizer', '').strip()
         if san:
             self.compile_flags += ['-fno-omit-frame-pointer']
+            if not sys.platform.startswith('freebsd'):
+                self.link_flags += ['-ldl']
             if san == 'Address':
                 self.compile_flags += ['-fsanitize=address']
                 self.config.available_features.add('asan')