Updates for building on Win32 with Visual C++ 2005 Express Edition

Updates for building on Win32 with Visual C++ 2005 Express Edition

Add some instructions in README.win32, clarify macro comments and add
missing macros to makefile.mk, and drop the GLOBEXEBUILD macro from
Makefile--the Express Edition of Visual C++ 2005 is free and includes
setargv.obj, so there is no need to support the .NET 2.0 SDK compiler
which didn't include it.

Unfortunately, the build still doesn't work yet--my attempt got as far
as building extensions, but miniperl.exe crashed.  Hopefully this can
be sorted out soon.

p4raw-id: //depot/perl@28978