[libbacktrace] Declare external backtrace fns noinline

[libbacktrace] Declare external backtrace fns noinline

The backtrace functions backtrace_full, backtrace_print and backtrace_simple
walk the call stack, but make sure to skip the first entry, in order to skip
over the functions themselves, and start the backtrace at the caller of the
functions.

When compiling with -flto, the functions may be inlined, causing them to skip
over the caller instead.

Fix this by declaring the functions with __attribute__((noinline)).

2019-02-08  Tom de Vries  <tdevries@suse.de>

	* backtrace.c (backtrace_full): Declare with __attribute__((noinline)).
	* print.c (backtrace_print): Same.
	* simple.c (backtrace_simple): Same.

From-SVN: r268668