perlcritic: prohibit map and grep in void conext

Hi hackers,

In the patches for improving the MSVC build process, I noticed a use of
`map` in void context.  This is considered bad form, and has a
perlcritic policy forbidding it:
https://metacpan.org/pod/Perl::Critic::Policy::BuiltinFunctions::ProhibitVoidMap.

Attached is a patch that increases severity of that and the
corresponding `grep` policy to 5 to enable it in our perlcritic policy,
and fixes the one use that had already snuck in.

- ilmari