All FreeBSD platforms are elf: move i386-elf to i386

This was a leftover from when we had both i386 a.out and ELF.

Reviewed by:	kib, imp
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D2591

lib/csu/Makefile

@@ -1,8 +1,7 @@
 # $FreeBSD$
 
-ARCH= ${MACHINE_ARCH:S/i386/i386-elf/}
-.if exists(${.CURDIR}/${ARCH})
-SUBDIR+= ${ARCH}
+.if exists(${.CURDIR}/${MACHINE_ARCH})
+SUBDIR+= ${MACHINE_ARCH}
 .else
 SUBDIR+= ${MACHINE_CPUARCH}
 .endif