Refactor t/globs.t to avoid the side effects of a change to strict.pm

Refactor t/globs.t to avoid the side effects of a change to strict.pm

As of blead commit b50b20584a1bbc1a, Implement new 'use 5.xxx' plan,
use strict; will write to %^H. Move the eval that creates the subroutine
into a different scope, a new subroutine generate_glob(), so that its
outside pointer chain doesn't include gv_grew(). This avoids problems with
eval ops changing the side of the %^H copies at runtime.