Remove unsupported symbol 'signal' from newlib exports.
Remove unsupported symbol 'signal' from newlib exports.

'signal' is part of libnosys.a, should be used from there.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/7604041

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@6395 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,sbc100/native_client,sbc100/native_client,nacl-webkit/native_client,sbc100/native_client,nacl-webkit/native_client