Revert "Don't internalize __truncxfhf2 for x86"

Bug: http://b/26165616 I had forgotten to revert this change when closing the bug. 

This reverts commit 10f2a8f1d60724c306d01cdd0682e38122637502.

Change-Id: Ic967b1965c2f7ca8fc74122a365e2b075704727a
Test: RsTest and CTS pass on x86 emulator.  small_struct test fails with
the same signature as b/29154200 - so unrelated to this CL.
1 file changed