Fix problems with finishing a dummy function call on simulators.

Fix problems with finishing a dummy function call on simulators.

Some simulators don't handle permanent breakpoints properly and will
sometimes terminate when hitting such a breakpoint instruction or have
unwanted effects.

When a permanent breakpoint is inserted, GDB will not attempt to insert
other breakpoint locations on top of it, leading to the problem described
above.

By not marking permanent breakpoint locations as inserted, we allow the
insertion of breakpoint locations on top of the permanent ones, preventing
the simulators from running into that situation.

gdb/ChangeLog:

2015-06-17  Luis Machado  <lgustavo@codesourcery.com>

	* breakpoint.c (add_location_to_breakpoint): Don't mark permanent
	locations as inserted.
	Update and expand comment about permanent locations.
	(bp_loc_is_permanent): Don't return 0 for bp_call_dummy.
	Move comment to add_location_to_breakpoint.
	(update_global_location_list): Don't error out if a permanent
	breakpoint is not marked inserted.
	Don't error out if a non-permanent breakpoint location is inserted on
	top of a permanent breakpoint.