pnacl-ld: Set ARM bitcode link --oformat target to nacl variant
pnacl-ld: Set ARM bitcode link --oformat target to nacl variant

gold does not recognize the non-nacl format variants (e.g. elf32-littlearm),
and emits a non-fatal error for arm-flavored bitcode link steps (e.g. for
direct-to-native builds with -arch and nonsfi mode).

R=mseaborn@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/720523002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@14083 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client