Add workaround for LLVM crash in macOS 12 on Intel or M1.

The `break_loop` test causes LLVM to get confused and crash when
compiled on some GPUs. The crash goes away if we pass a literal 5
instead of a 5 that is computed at runtime. This also results in a
simpler test for SkVM, for better or worse, but we still have
coverage for dynamic loop exits in other tests.

LLVM crash: https://paste.googleplex.com/4718583155261440
Dangerous shader: https://paste.googleplex.com/4776089520963584

Change-Id: Ic6cbd55a36d2de58e5dd3459d4dfd74acdbc9f91
Bug: skia:13005
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/514538
Reviewed-by: Arman Uguray <armansito@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
5 files changed