[llvm] [AArch64] Enable "sink-and-fold" in MachineSink by default (PR #67432)

[Momchil Velikov via llvm-commits]

momchil-velikov wrote:

Small reproducer here:
```
int f(int);

void g(int x) {
  int y = x + 1;

  int t0 = y;
  f(t0);

  int t1 = y;
  f(t1);
}
```

With these commands
```
#! /bin/bash

./bin/clang -target aarch64-linux -g -O2 -S ccc.c -emit-llvm
./bin/llc  ccc.ll --aarch64-enable-sink-fold=true --stop-before=machine-sink -o ccc-before.mir
./bin/llc  ccc.ll --aarch64-enable-sink-fold=true --stop-after=machine-sink -o ccc-after.mir
kdiff3 ccc-{before,after}.mir
```
it's quite evident how sink-and-fold causes quadratic explosion in the number the DBG_VALUE instructions.


https://github.com/llvm/llvm-project/pull/67432