Remove dwarf2_per_cu_data::mark

Remove dwarf2_per_cu_data::mark

This removes dwarf2_per_cu_data::mark, replacing it with a
locally-allocated boolean vector.  It also inverts the sense of the
flag -- now, the flag is true when a CU should be skipped, and false
when the CU should be further examined.  Also, the validity of the
flag is no longer dependent on 'file_matcher != NULL'.

This patch makes the subsequent patch to searching a bit simpler, so
I've separated it out.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16994
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=16998
Acked-By: Simon Marchi <simon.marchi@efficios.com>