File::Glob: Dup glob state in CLONE()

This solves [perl #119897] and [perl #117823], and restores the
behavior of glob() in conjunction with threads of 5.14 and older.

Since 5.16, code that used glob() inside a thread had been
unintentionally sharing state between threads, which lead to things
like this crashing and failing assertions:

./perl -Ilib -Mthreads -e 'scalar glob("*"); threads->create(sub { glob("*") })->join();'