Add check_effective_target_gettimeofday and use it in gcc.dg/lto/pr60449_0.c.

Add check_effective_target_gettimeofday and use it in gcc.dg/lto/pr60449_0.c.

gcc/
	* doc/sourcebuild.texi (Effective-Target Keywords, Environment
	attributes): Document gettimeofday.

gcc/testsuite/

	* gcc.dg/lto/pr60449_0.c: Add dg-require-effective-target for
	gettimeofday.  Remove dg-skip-if for AVR.
	* lib/target-supports.exp (check_effective_target_gettimeofday):
	New proc.

From-SVN: r245921