Parrot's Configure routine uses your Perl5 compiler info as a starting point. Everything inherited from the Perl5 environment is overrideable. Parrot will often be built in environments where the compilers for Parrot and Perl5 differ; Configure.pl and friends have support for this. See my post below for more details. My personal goal for the free Win32 compiler support is an auto-recognition routine in Configure.pl, but no tuits yet.