[compiler-rt] [llvm] [HWASan][Fuchsia] Have Fuchsia use a dynamic shadow start (PR #180881)

[Roland McGrath via llvm-commits]

https://github.com/frobtech approved this pull request.

The compiler and runtime changes should be separate and just ordered appropriately.

We can safely land the compiler change with no runtime changes as things stand.  So we should do that first.  Then we can follow up on the details of the runtime changes.

https://github.com/llvm/llvm-project/pull/180881