[mlir][acc] Add ACCIfClauseLowering pass (#173447)
This pass lowers OpenACC compute constructs with `if` clauses into
`scf.if` with separate device and host paths.
Before:
```
%d = acc.copyin varPtr(%a : memref<10xf32>) -> memref<10xf32>
acc.parallel dataOperands(%d) if(%cond) {
acc.loop control(%i : i32) = (%c0 : i32) to (%c10 : i32) step (%c1 :
i32) {
// loop body
acc.yield
}
acc.yield
}
acc.copyout accPtr(%d) to varPtr(%a)
```
After:
```
scf.if %cond {
%d = acc.copyin varPtr(%a : memref<10xf32>) -> memref<10xf32>
acc.parallel dataOperands(%d) {
acc.loop control(%i : i32) = (%c0 : i32) to (%c10 : i32) step (%c1
: i32) {
// loop body
acc.yield
}
acc.yield
}
acc.copyout accPtr(%d) to varPtr(%a)
} else {
scf.for %i = %c0 to %c10 step %c1 {
// loop body
}
}
```
Co-authored-by: Susan Tan <zujunt@nvidia.com>
