Change type of dwarf_lock from rwlock to mutex

Change type of dwarf_lock from rwlock to mutex

Change type of dwarf_lock to mutex in order to take advantage of
built-in support for recursive locking.

	* lib/locks.h: Add macros for locking, unlocking, initializing
	and destroying mutexes.
	* libdw/dwarf_begin_elf.c (dwarf_end): Replace rwlock macro with
	mutex macro.
	* libdw/dwarf_formref_die.c (dwarf_formref_die): Ditto.
	* libdw/dwarf_getalt.c (dwarf_getalt): Ditto.
	* libdw/dwarf_setalt.c (dwarf_setalt): Ditto.
	* libdw/libdwP.h (struct Dwarf): Ditto.
	* libdw/libdw_findcu.c (__libdw_findcu): Ditto.

Signed-off-by: Aaron Merey <amerey@redhat.com>