String benchtest cleanup

Continue cleanup of the string benchtests.  Remove simplistic
byte-oriented versions with faster generic implementations.
Remove bcopy/bzero benchmarks (bcopy/bzero are obsolete and never
emitted by compilers).  Remove builtin versions of memcpy, memset
and strlen.  Remove all remaining "stupid" implementations given
they are always slower than the "simple" variants and thus don't
add anything useful.

	* benchtests/bench-strcasecmp.c (stupid_strcasecmp): Remove.
	* benchtests/bench-strcasestr.c (stupid_strcasestr): Remove.
	* benchtests/bench-strchr.c (stupid_strchr): Remove.
	* benchtests/bench-strcmp.c (stupid_strcmp): Remove.
	* benchtests/bench-strcspn.c (stupid_strcspn): Remove.
	* benchtests/bench-strlen.c (builtin_strlen): Remove.
	* benchtests/bench-strncasecmp.c (stupid_strncasecmp): Remove.
	* benchtests/bench-strncmp.c (stupid_strncmp): Remove.
	* benchtests/bench-strpbrk.c (stupid_strpbrk): Remove.
	* benchtests/bench-strspn.c (stupid_strspn): Remove.
	* benchtests/Makefile: Remove bench-bcopy.c and bench-bzero.c.
	* benchtests/bench-bcopy.c: Delete file.
	* benchtests/bench-bzero.c: Likewise.
	* benchtests/bench-memccpy.c (stupid_memccpy): Remove.
	(simple_memccpy): Remove.
	(generic_memccpy): Add function.
	* benchtests/bench-memcpy.c: (builtin_memcpy): Remove.
	* benchtests/bench-memmove.c (simple_bcopy): Remove.
	* benchtests/bench-mempcpy.c (simple_mempcpy): Remove.
	(generic_mempcpy): Add new function.
	* benchtests/bench-memset.c (simple_bzero): Remove.
	(builtin_bzero): Remove.
	(builtin_memset): Remove.
	* benchtests/bench-rawmemchr.c (simple_rawmemchr): Remove.
	(generic_rawmemchr): Add new function.