Blind attempt to fix MSVC pgcrypto build.

Blind attempt to fix MSVC pgcrypto build.

Commit db7d1a7b0 pulled out Mkvcbuild.pm's custom support for building
contrib/pgcrypto, but neglected to inform it that that module can now
be built normally.  Or at least I guess it can now be built normally.
But this is definitely causing bowerbird to fail, since it's trying to
test a module it hasn't built.