Previously instructions-arm64.h was alternatively defining or declaring
some constants based on whether or not ARM64_DEFINE_FP_STATICS was defined,
and it was assumed that exactly one file would include this header with
the macro defined.

In jumbo builds, the header guards in instructions-arm64.h meant that the
resulting state of the header file would be whichever of the two cases
that appeared first in the compilation unit.  This would cause multiple
definitions in some cases and no definitions in some other cases (or if
you were really lucky, it would work out ok).

Let's move these constants to a separate source file temporarily, to be
excluded from jumbo compilation units.  This code should eventually be
replaced with a cleaner solution.

Bug: chromium:746958
Change-Id: I7edb1821ef408afd50c6b236d63d3c07f955b58f
Reviewed-on: https://chromium-review.googlesource.com/663898
Commit-Queue: Mostyn Bramley-Moore <mostynb@opera.com>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48003}