gdb: add all_breakpoints_safe function

gdb: add all_breakpoints_safe function

Same as the previous patch, but intended to replace the
ALL_BREAKPOINTS_SAFE macro, which allows deleting the current breakpoint
while iterating.  The new range type simply wraps the range added by the
previous patch with basic_safe_range.

I didn't remove the ALL_BREAKPOINTS_SAFE macro, because there is one
spot where it's more tricky to remove, in the
check_longjmp_breakpoint_for_call_dummy function.  More thought it
needed for this one.

gdb/ChangeLog:

	* breakpoint.c (breakpoint_safe_range): New.
	(all_breakpoints_safe): New.  Use instead of
	ALL_BREAKPOINTS_SAFE where possible.

Change-Id: Ifccab29f135e1f85700e3697ed60f0b643c7682f