re PR other/67457 (segfault in libbacktrace)

re PR other/67457 (segfault in libbacktrace)

	PR other/67457
	* backtrace.c: #include "internal.h".
	(struct backtrace_data): Add can_alloc field.
	(unwind): If can_alloc is false, don't try to get file/line
	information.
	(backtrace_full): Set can_alloc field in bdata.
	* alloc.c (backtrace_alloc): Don't call error_callback if it is
	NULL.
	* mmap.c (backtrace_alloc): Likewise.
	* internal.h: Update comments for backtrace_alloc and
	backtrace_free.

From-SVN: r227533