Fix test-strchr.c warnings for wide string testing.

Fix test-strchr.c warnings for wide string testing.

string/test-strchr.c is used for both wide and narrow string testing,
but produces a series of warnings for wide string testing because of
hardcoded use of narrow characters in the function check1.  This patch
fixes that function to use macros abstracting away the wide / narrow
string choice, adding a new such macro to handle the string and
character constants.

Tested for x86_64.

	* string/test-strchr.c [!WIDE] (L): New macro.
	[WIDE] (L): Likewise.
	(check1): Use CHAR instead of char.  Use L on string and character
	constants.