unix: add ppc64le/linux support

This incorporates changes from https://golang.org/cl/123290043 and
https://golang.org/cl/127320043.

Files generated on Ubuntu Trusty.

Change-Id: I669c60714e857ef5f06515cd3b65dfc94785e179
Reviewed-on: https://go-review.googlesource.com/10060
Reviewed-by: Rob Pike <r@golang.org>

unix/mkerrors.sh

@@ -255,6 +255,7 @@ ccflags="$@"
 		$2 ~ /^(SIGEV_|SIGSTKSZ|SIGRT(MIN|MAX))/ {next}
 		$2 ~ /^(SCM_SRCRT)$/ {next}
 		$2 ~ /^(MAP_FAILED)$/ {next}
+		$2 ~ /^ELF_.*$/ {next}# <asm/elf.h> contains ELF_ARCH, etc.
 
 		$2 ~ /^EXTATTR_NAMESPACE_NAMES/ ||
 		$2 ~ /^EXTATTR_NAMESPACE_[A-Z]+_STRING/ {next}