For the RX port, avoid using string instructions when __RX_DISALLOW_STRING_INSNS__...

For the RX port, avoid using string instructions when __RX_DISALLOW_STRING_INSNS__ is defined.

	* rx/crt0.S (_start): If string instructions are not allowed,
	avoid using SMOVF.

	* libc/machine/rx/memchr.S: Add non-string insn using version.
	* libc/machine/rx/memcpy.S: Likewise.
	* libc/machine/rx/memmove.S: Likewise.
	* libc/machine/rx/mempcpy.S: Likewise.
	* libc/machine/rx/strcat.S: Likewise.
	* libc/machine/rx/strcmp.S: Likewise.
	* libc/machine/rx/strcpy.S: Likewise.
	* libc/machine/rx/strlen.S: Likewise.
	* libc/machine/rx/strncat.S: Likewise.
	* libc/machine/rx/strncmp.S: Likewise.
	* libc/machine/rx/strncpy.S: Likewise.