See the current Perl documentation for ExtUtils::MM_OS2.

Here is our local, out-dated (pre-5.6) version:

ExtUtils::MM_OS2 - methods to override UN*X behaviour in ExtUtils::MakeMaker

 use ExtUtils::MM_OS2; # Done internally by ExtUtils::MakeMaker if needed

See ExtUtils::MM_Unix for a documentation of the methods provided there. This package overrides the implementation of these methods, not the semantics.