Revert workaround for long vixl compile times.

This no longer takes that long to compile, although there is still some
room for improvement. The bug will have more details on how to improve
the existing source code to do exactly that.

Bug: http://b/73087272
Test: Build vixl tests from scratch in < 3 minutes.
Change-Id: If3072ec5ecd976df1c2af35b9f297b5d57cc1056