Print markers to stderr to avoid races with sanitizer output

Print markers to stderr to avoid races with sanitizer output

	* c-c++-common/asan/swapcontext-test-1.c,
	* c-c++-common/tsan/thread_leak.c,
	* g++.dg/tsan/aligned_vs_unaligned_race.C,
	* g++.dg/tsan/benign_race.C,
	* g++.dg/tsan/fd_close_norace.C,
	* g++.dg/tsan/fd_close_norace2.C: Print markers to stderr to avoid
	races with sanitizer output

From-SVN: r233899