GLIBC uses strchr (s, '\0') as an idiom to find the end of a string.

GLIBC uses strchr (s, '\0') as an idiom to find the end of a string.
This is transformed into rawmemchr by the bits/string2.h header.
However this is generally slower than strlen on most targets, even when
an optimized rawmemchr implementation exists.  Since GCC7 optimizes
strchr (s, '\0') to strlen (s) + s, the GLIBC headers should not
transform this to rawmemchr.  As GCC recognizes strchr as a builtin,
defining strchr as the builtin is not useful.

	* string/bits/string2.h (strchr): Remove define.