Add gyp build of sel_ldr and irt_core for ARM.
Add gyp build of sel_ldr and irt_core for ARM.

The irt core can be built on all platforms but sel_ldr
can only be built on linux (the only platform with an
arm cross compiler).

BUG=266959
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/93513013

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@12589 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

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