C:\mercurial\mercurial-stable>set PATH=C:\mingw-rvb\bin;%PATH%

C:\mercurial\mercurial-stable>echo %PATH%
C:\mingw-rvb\bin;C:\Program Files\CollabNet\Subversion Client;C:\Windows\system32;C:\Windows;
C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\ATI Technologies\ATI.ACE\Core-Static;
C:\Program Files\Microsoft Windows Performance Toolkit\;C:\tools;C:\Python27\Scripts;C:\Python27;
C:\ruby192\bin;c:\scala\bin;c:\lua\bin;c:\groovy\bin;C:\gnuwin32\curl\bin;C:\gnuwin32\diff\bin;C:\gnuwin32\grep\bin;
C:\gnuwin32\findutils\bin;C:\gnuwin32\sed\bin;C:\gnuwin32\gawk\bin;C:\gnuwin32\less\bin;C:\gnuwin32\upx\bin;
C:\gnuwin32\coreutils\bin;C:\Program Files\Wix;C:\git\cmd

C:\mercurial\mercurial-stable>gcc --version
gcc (GCC) 4.6.2 20110705 (prerelease)
Copyright (C) 2011 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

C:\mercurial\mercurial-stable>type setup.cfg
[build_ext]
inplace = 1
compiler = mingw32

C:\mercurial\mercurial-stable>python setup.py build
running build
running build_mo
warning: hgbuildmo: could not find msgfmt executable, no translations will be built

running build_py
creating build
creating build\lib.win32-2.7
creating build\lib.win32-2.7\mercurial
copying mercurial\ancestor.py -> build\lib.win32-2.7\mercurial
...
...SNIP...
...
running build_ext
building 'mercurial.base85' extension
creating build\temp.win32-2.7
creating build\temp.win32-2.7\Release
creating build\temp.win32-2.7\Release\mercurial
C:\mingw-rvb\bin\gcc.exe -mno-cygwin -mdll -O -Wall -IC:\Python27\include -IC:\Python27\PC -c mercurial/base85.c -o build\temp.win32-2.7\Release\mercurial\base85.o
cc1.exe: error: unrecognized command line option '-mno-cygwin'
error: command 'gcc' failed with exit status 1