Only create ARM untrusted env for validator testing when needed.
Only create ARM untrusted env for validator testing when needed.

The untrusted env getter asserts that arch != mips, but that could
happen on the mips bots.

BUG= red toolchain bot:

http://build.chromium.org/p/client.nacl.toolchain/builders/linux-pnacl-x86_32-tests-mips/builds/482/steps/compile_toolchain/logs/stdio#error1

TEST= ./scons bitcode=1 run_arm_test_external_jumps platform=arm

Review URL: https://codereview.chromium.org/11677005

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@10511 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client