llvm-rc: accept /D, /U, /I parameters joined or separate like rc.exe

[awakecoding]

Summary

This change adds support for joined parameters for /D, /U and /I options like rc.exe, and fixes a problem encountered while trying to cross-compile from Linux to Windows using a custom cmake toolchain, ninja, llvm-rc, and MSVC headers + libraries extracted from the Visual Studio 2019 build tools.

As far as I know, CMake doesn't know it's calling llvm-rc on Linux, and generates the same command-line arguments it would normally feed to rc.exe on Windows. It should also be noted that in order to get partial success cross-compiling using llvm-rc, I had to patch my .rc scripts and make a minor modification to CMake to disable the cmcldeps wrapper. Patching llvm-rc to accept the arguments as joined worked around the problem that CMake generated the command-line parameters as joined, which works with rc.exe but not with llvm-rc.

A very similar change has been done for similar reasons for the /fo flag, but didn't apply the change to /D, /U and /I: https://reviews.llvm.org/D54191

This is my first contribution to LLVM, so feel free to request anything necessary to fit within the contribution guidelines.

[mstorsjo]

Please add testcases for these changes. You could e.g. change some of the existing tests in test/tools/llvm-rc so that both forms are exercised, or add a new test there that uses that form.

llvm/tools/llvm-rc/Opts.td

 include "llvm/Option/OptParser.td"
 
 // All the switches can be preceded by either '/' or '-'.
 // These options seem to be important for the tool
 // and should be implemented.
 
 def FILEOUT : JoinedOrSeparate<[ "/", "-" ], "FO">,
               HelpText<"Change the output file location.">;
 
-def DEFINE : Separate<[ "/", "-" ], "D">,
+def DEFINE : JoinedOrSeparate<[ "/", "-" ], "D">,
              HelpText<"Define a symbol for the C preprocessor.">;
-def UNDEF : Separate<[ "/", "-" ], "U">,
+def UNDEF : JoinedOrSeparate<[ "/", "-" ], "U">,
             HelpText<"Undefine a symbol for the C preprocessor.">;
 
 def LANG_ID : Separate<[ "/", "-" ], "L">,
               HelpText<"Set the default language identifier.">;
 def LANG_NAME : Separate<[ "/", "-" ], "LN">,
                 HelpText<"Set the default language name.">;
 
-def INCLUDE : Separate<[ "/", "-" ], "I">, HelpText<"Add an include path.">;
+def INCLUDE : JoinedOrSeparate<[ "/", "-" ], "I">, HelpText<"Add an include path.">;
 def NOINCLUDE : Flag<[ "/", "-" ], "X">, HelpText<"Ignore 'include' variable.">;
 
 def ADD_NULL : Flag<[ "/", "-" ], "N">,
                HelpText<"Null-terminate all strings in the string table.">;
 
 def DUPID_NOWARN : Flag<[ "/", "-" ], "Y">,
                    HelpText<"Suppress warnings on duplicate resource IDs.">;