[PATCH 07 of 10 V5] rcutil: let environ override system configs (BC)

[Jun Wu]

Excerpts from Matt Harbison's message of 2017-04-07 00:35:42 -0400:
> > Just to confirm: if you run "make local", it will say "cl.exe ..."  
> > instead
> > of "gcc ..." (where gcc could come from MinGW).
> 
> Yep.
> 
> $ make local | grep cl.exe
> c:\Program Files (x86)\Microsoft Visual Studio 9.0\VC\BIN\amd64\cl.exe /c  
> /nologo /Ox /MD /W3 /GS- /DNDEBUG -Ic:\Python27\include -Ic:\Python27\PC  
> /Tcmercurial/bdiff.c  
> /Fobuild\temp.win-amd64-2.7\Release\mercurial/bdiff.obj
> ...
> 
> > And you are using Python for
> > Windows, not some cygwin or mingw Python.
> 
> Correct.  2.7.13, from the python.org Windows installer.
> 
> > And the shell is provided by MinGW.
> 
> I've never had cygwin or anything else installed.  The titlebar says  
> "MINGW32", and $SHELL is /bin/sh.  Not sure if there's something specific  
> I should check here.

Thanks. I have sent a fix.