Clean up duplicated signal number list by using NACL_ARRAY_SIZE
Clean up duplicated signal number list by using NACL_ARRAY_SIZE

This requires changing some index types to avoid warnings.

Also switch from "#ifdef SIGSTKFLT" to "#if OS_LINUX" because feature
tests are not the usual style in the NaCl codebase, and the latter
makes it clearer to the reader when the conditional will apply.

BUG=none
TEST=build

Review URL: https://chromiumcodereview.appspot.com/10383079

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@8530 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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