Adds support for hoisting `writeonly` calls in LICM.
This patch adds a missing optimization that allows hoisting of
`writeonly` function calls out of loops when it is safe to do so.
Previously, such calls were conservatively retained inside the loop
body, and the redundant calls were only reduced through unrolling,
relying on target-dependent heuristics.
Closes#143267
Testing:
- Modified previously negative tests for hoisting writeonly calls to be
instead positive
- Added test cases for hoisting of two writeonly calls where the
pointers do/do not alias
- Added a test case for not argmemonly writeonly calls.
1ab0e7dd60