Pass instruction set variant to dex2oat.

Also, add it to the ANDROID_BUILD_PROPERTIES.
Remove non-default instruction set features.
Bug: 18056890

Change-Id: I9169cdfecbb176f62b941852948222edc3f511fd
kill HAVE_FORKEXEC

Bug: 18317407
Change-Id: Idaff8a161305325dbb0a9e00764afe98b66e3312
Merge "kill HAVE_FORKEXEC"
Merge "Pass instruction set variant to dex2oat."