Automatic RC handling for GNAT

Gnatlink does not automatically handle the resource (.rc) files common
in Windows programs.  Wglink rectifies this.  It is a shell that
automatically processes any.rc or any.res files that were mentioned
in a Pragma Linker_Options("any.rc"), or, with Gnat 3.15,
Pragma Link_With("any.rc"), producing .rbj files, then it calls
gnatlink with the linker options changed to "any.rbj".

To use wglink, add appropriate 'pragma linker_options("abc.rc")'
to the Ada source code, then add "--GNATLINK=wglink.exe" to your
gnatmake command line.

By default, wglink uses rcl.exe and res2coff, as needed.  If rcl
is inadequate for your .rc file, and you have rc.exe available,
then add "--RC" to the gnatmake command line to use rc.exe instead.