goarch.bbclass: set SECURITY_CFLAGS for mips64
When include conf/distro/include/security_flags.inc, NOPIE flags are
still required for mips64 target builds. Otherwise it fails to build
packages such as glide which inherit go.bbclass:
| .../tmp-glibc/work/mips64-wrs-linux/glide/0.13.1-r0/recipe-sysroot-native/usr/bin/mips64-wrs-linux/../../libexec/mips64-wrs-linux/
| gcc/mips64-wrs-linux/7.3.0/ld: .../tmp-glibc/work/mips64-wrs-linux/glide/0.13.1-r0/go-tmp/go-link-
518447869/go.o:
| relocation r_mips_26 against `a local symbol' can not be used when making a shared object; recompile with -fPIC`
Use override 'mipsarch' to set SECURITY_CFLAGS for both mips and mips64.
Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
