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.