Adjust benchtests to new support library.

This patch basically replaces the test-skeleton.c inclusion by
support/test-driver.c and also minor adjustments in bench-string.h.

Checked on x86_64-linux-gnu and powerpc64le-linux-gnu.

	* benchtests/bench-string.h (TEST_FUNCTION): Use name without
	parenthesis.
	(CMDLINE_PROCESS): Define using function instead of macro.
	* benchtests/bench-memccpy.c: Include <support/test-driver.c> instead
	of test-skeleton.
	* benchtests/bench-memchr.c: Likewise.
	* benchtests/bench-memcmp.c: Likewise.
	* benchtests/bench-memcpy-large.c: Likewise.
	* benchtests/bench-memcpy.c: Likewise.
	* benchtests/bench-memmem.c: Likewise.
	* benchtests/bench-memmove-large.c: Likewise.
	* benchtests/bench-memmove.c: Likewise.
	* benchtests/bench-memset-large.c: Likewise.
	* benchtests/bench-memset.c: Likewise.
	* benchtests/bench-rawmemchr.c: Likewise.
	* benchtests/bench-strcasecmp.c: Likewise.
	* benchtests/bench-strcasestr.c: Likewise.
	* benchtests/bench-strcat.c: Likewise.
	* benchtests/bench-strchr.c: Likewise.
	* benchtests/bench-strcmp.c: Likewise.
	* benchtests/bench-strcpy.c: Likewise.
	* benchtests/bench-strcpy_chk.c: Likewise.
	* benchtests/bench-strlen.c: Likewise.
	* benchtests/bench-strncasecmp.c: Likewise.
	* benchtests/bench-strncmp.c: Likewise.
	* benchtests/bench-strncpy.c: Likewise.
	* benchtests/bench-strnlen.c: Likewise.
	* benchtests/bench-strpbrk.c: Likewise.
	* benchtests/bench-strrchr.c: Likewise.
	* benchtests/bench-strsep.c: Likewise.
	* benchtests/bench-strspn.c: Likewise.
	* benchtests/bench-strstr.c: Likewise.
	* benchtests/bench-strtok.c: Likewise.