Use generic_category from the std namespace.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210736 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Basic/VirtualFileSystem.cpp

@@ -140,7 +140,7 @@ error_code RealFile::getBuffer(const Twine &Name,
 #endif
 error_code RealFile::close() {
   if (::close(FD))
-    return error_code(errno, generic_category());
+    return error_code(errno, std::generic_category());
   FD = -1;
   return error_code();
 }