ART: remove nested include in arch_test

arch_test #includes asm_support.h while inside the art namespace.
We've gotten away with this until now because the files that
asm_support.h includes had already been included earlier (and thus,
were empty via the #ifdef guard).  However, adding new #includes to
asm_support.h results in art::art:: namespace ugliness.

Change-Id: Ie2671c456bb631976b4280f29a5656b086138047