cext: define MIN macro only if it is not yet defined
MIN macro is defined in <sys/param.h> on macOS Sierra. Therefore as
HAVE_BSD_STATFS is defined in osutil.c, 'MIN' macro redefined warning is
emitted.
Welcome to Mercurial for Windows!
---------------------------------
For configuration and usage directions, please read the ReadMe.html
file that comes with this package.
Also check the release notes at:
https://mercurial-scm.org/wiki/WhatsNew