Re-enable the coff-dwarf test on Windows

Apparently system-windows was only a clang lit suite feature.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249797 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rnk

test/lit.cfg

@@ -443,6 +443,10 @@ if 'darwin' == sys.platform:
         config.available_features.add('fma3')
     sysctl_cmd.wait()
 
+if platform.system() in ['Windows']:
+    # For tests that require Windows to run.
+    config.available_features.add('system-windows')
+
 # .debug_frame is not emitted for targeting Windows x64.
 if not re.match(r'^x86_64.*-(mingw32|windows-gnu|win32)', config.target_triple):
     config.available_features.add('debug_frame')