Perform the loop-exit test when continuing from inside a do-while.

SPIR-V would previously jump to the top of the do-while loop when
encountering a `continue`. This is not correct; it should jump to the
loop-exit test. We don't have any real shaders which test this case, and
it can't be checked from inside Runtime Effects since do-while is not
part of ES2.

Change-Id: Iac58e9e7ad0a94640e6418afea096b19ba50a2df
Bug: skia:11874
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/397576
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
6 files changed