Allow additions to PERL_MB_OPT

[djerius]

Some distributions have custom Module::Build options that need to be applied, but cpm overrides the PERL_MB_OPT variable.

For example, Params::Validate v1.29 doesn't recognize --pureperl_only, but does recognize --pp.

I'd like to be able to do something equivalent to this:

PERL_MB_OPT=--pp cpan Params::Validate

Thanks, Diab

[skaji]

For --pureperl-only, it is defined in The Lancaster Consensus.

[djerius]

Agreed, it's just that there are older modules which don't support it yet, so the ability to add options to Build.PL would be useful.

[skaji]

Actually, I thought cpm respected PERL_MM_OPT. But, it turns out that local::lib overwrite the environment variable.