Previously all unsandboxed 64-bit code was assumed to use ILP32 and
be stored in ELF32 format using the x32 ABI.

BUG=swiftshader:9

Change-Id: I2476a09d1f0af60b1ac6f8807ee9ed37d54a99d4
Reviewed-on: https://chromium-review.googlesource.com/385277Reviewed-by: Jim Stichnoth <stichnot@chromium.org>
Tested-by: Nicolas Capens <nicolascapens@google.com>