[ARM][Testsuite]make dump_stack function call conditional in cold-lc.c

[ARM][Testsuite]make dump_stack function call conditional in cold-lc.c

After r249013, die () and dump_stack () are both in cold section. This makes
the compiler generate bl instruction for the function call, instead of
honoring the -mlong-calls option.

This patch changes the dump_stack function call conditional, which fixes the
regression.

gcc/testsuite/

	* gcc.target/arm/cold-lc.c: Update coding style, call dump_stack
	conditionally.

From-SVN: r249157