PR go/65349

	PR go/65349
runtime: Don't call malloc from __go_file_line callback.

When crashing, we call runtime_printcreatedby which calls
__go_file_line which used to call the Go malloc.  If we are
crashing due to a signal due to heap corruption of some sort,
the GO malloc lock might already be held, leading to a crash
within a crash.  Avoid that by assuming that the libbacktrace
strings will stick around, as we already do in go-callers.c.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@221291 138bc75d-0d04-0410-961f-82ee72b054a4