[testsuite/guality] Use line number vars in gdb-test

[testsuite/guality] Use line number vars in gdb-test

2018-06-29  Tom de Vries  <tdevries@suse.de>

	* gcc.dg/guality/pr45882.c (foo): Add line number var for breakpoint
	line, and use it.
	* lib/gcc-dg.exp (get-absolute-line): Factor out of ...
	(process-message): ... here.
	* lib/gcc-gdb-test.exp (gdb-test): Use get-absolute-line.

From-SVN: r262248