[llvm-rc] Support joined or separate spelling for /fo flag

CMake invokes rc using the joined spelling which appears to be supported
by Microsoft's rc implementation, so we should support it as well.

Differential Revision: https://reviews.llvm.org/D54191

llvm-svn: 346470
diff --git a/llvm/tools/llvm-rc/Opts.td b/llvm/tools/llvm-rc/Opts.td
index 11f40f5..3ff5ac2 100644
--- a/llvm/tools/llvm-rc/Opts.td
+++ b/llvm/tools/llvm-rc/Opts.td
@@ -4,7 +4,7 @@
 // These options seem to be important for the tool
 // and should be implemented.
 
-def FILEOUT : Separate<[ "/", "-" ], "FO">,
+def FILEOUT : JoinedOrSeparate<[ "/", "-" ], "FO">,
               HelpText<"Change the output file location.">;
 
 def DEFINE : Separate<[ "/", "-" ], "D">,