Don't use ARM sysroot in gyp builds.
Don't use ARM sysroot in gyp builds.

This fixes the NaCl SDK build on Ubuntu/Trusty.

This change was aleady made to the scons build here:
https://codereview.chromium.org/427953002

R=mseaborn@chromium.org

Review URL: https://codereview.chromium.org/486303002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13637 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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