Use atomic load/store to access static backtrace state pointer

As the static backtrace state pointer can be accessed from multiple
threads, use atomics to access it.

Regtested on x86_64-pc-linux-gnu.

libgfortran/ChangeLog:

2018-12-02  Janne Blomqvist  <jb@gcc.gnu.org>

        Backport from trunk
	PR libfortran/88137
	* runtime/backtrace.c (show_backtrace): Use atomic load/store to
	access the static lbstate pointer.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/branches/gcc-8-branch@266725 138bc75d-0d04-0410-961f-82ee72b054a4
2 files changed