[libbacktrace] Add btest_lto

Add libbacktrace test-case using -flto.

2019-02-10  Tom de Vries  <tdevries@suse.de>

	* Makefile.am (BUILDTESTS): Add btest_lto.
	* Makefile.in: Regenerate.
	* btest.c (test1, f2, f3, test3, f22, f23): Declare with
	__attribute__((noclone)).

From-SVN: r268736