Disable AVX support in bcc

Bug: 28879581

LLVM generates AVX code for long3 load/store, which treats a long3 value
as 256 bits, while the RS runtime only allocates 192 bits for a long3
element in an allocation.

This CL disables AVX codegen to avoid this issue.

Change-Id: Ia656a36c35a4cfbe620a555abb8b28c808843459
1 file changed