Bug 1892549: Don't scan lib/ for modules in Makefile.PL

[topunix]

Fixes make cpanfile failing with "multiple target patterns" when lib/ contains installed modules.

Cause

With no PM or PMLIBDIRS set, MakeMaker scans lib/ and Bugzilla/ (from NAME). Modules installed into lib/ by older tooling can have :: in their filenames, and those end up as make targets, which make rejects.

Fix

Set PMLIBDIRS => ['Bugzilla']. Bugzilla/ is scanned exactly as before; lib/ is skipped. Harmony installs Perl dependencies into local/, so nothing in lib/ is needed here.

This doesn't delete lib/ as suggested in the bug, since lib/README is tracked and would be removed on every run.

Testing

• Reproduced by adding lib/x/Foo::Bar.pm and running perl Makefile.PL && make cpanfile: fails with multiple target patterns.
• With the fix, the same file is no longer picked up in the generated Makefile's module lists, and make cpanfile gets past Makefile parsing.