* builtins.c (target_char_cast): New function.
	(expand_builtin_strchr): Use it.
	(expand_builtin_strrchr): Use it.
	(builtin_memset_read_str): New function.
	(expand_builtin_memset): Use target_char_cast.
	Try to optimize memset with second argument non-zero using
	store_by_pieces.

	* gcc.c-torture/execute/string-opt-5.c: Add some memset tests.

From-SVN: r37918