Check only for i386 version of GMP header
Check only for i386 version of GMP header

.. since we build only a 32bit toolchain, an x86_64 gmp header does not help in
that process.
Review URL: http://codereview.chromium.org/6660025

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@4495 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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