Split PERL_MB_OPT as on Unix

[Leont]

Currently in Module::Build and Module::Build::Tiny we're using platform specific splitting for PERL_MB_OPT, which means using Text::ParseWords on all platforms except Windows, where a custom and widely presumed buggy function is used.

There is no need for it to do this (it's not handled by a shell). local::lib isn't doing anything Windows specific there either as far as I understand.

Hence, I propose we change the behavior in the spec and in the implementations to using Unix semantics even on Windows, just like ExtUtils::MakeMaker is with PERL_MM_OPT.