This CL modifies the ARM32 backend so that the REGARM32_TABLE is only
expanded once (to initialize a constexpr array.) This change decreased
the backend size in roughly ~80k.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4076
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1554263002 .