allow running parts of src/tools/msvc/ under not Windows

When making build system changes that risk breaking the MSVC build 
system, it's useful to be able to run the part of the MSVC build tools 
that read the makefiles and produce the project files under a 
not-Windows platform.  This part does not really depend on anything 
particular to Windows, so it's possible in principle.  There are some 
minor dependencies on Windows, however, that need to be worked around. 
I have had some local hacks for that for a while, and I took a moment to 
clean them up and make them presentable, so here they are.  Interested?

To test, apply the patch and run perl src/tools/msvc/mkvcbuild.pl .

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
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