Fix frexp support in Metal.

Our Metal codegen assumes that out params are pointers, but Metal's
built-in frexp actually takes a reference for the exponent, not a
pointer. We now add in a helper function to translate.

Change-Id: I24686347d07151dd99a1ff1c43aff2b35c3181e5
Bug: skia:10762
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/328387
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
3 files changed