This patch introduces a new virtual method
`TargetInstrInfo::isSafeToMove()` to allow backends to control whether a
machine instruction can be safely moved by optimization passes.

The `BranchFolder` pass now respects this hook when hoisting common
code. By default, all instructions are considered safe to to move.

For LoongArch, `isSafeToMove()` is overridden to prevent
relocation-related instruction sequences (e.g. PC-relative addressing
and calls) from being broken by instruction motion. Correspondingly,
`isSchedulingBoundary()` is updated to reuse this logic for consistency.

Relands #163725

After overriding `TargetTransformInfo::enableMemCmpExpansion` in this
commit, `MergeICmps` and `ExpandMemCmp` passes will be enabled on
LoongArch.

Test cases are similar as riscv.

Add option `loongarch-enable-sink-fold` to enable sink-fold and set
`true` as default. This pass can fold `addi+load/store` to a single
`load/store` with offset.

This patch introduces the LASX and LSX conversion intrinsics:

- <8 x float> @llvm.loongarch.lasx.cast.128.s(<4 x float>)
- <4 x double> @llvm.loongarch.lasx.cast.128.d(<2 x double>)
- <4 x i64> @llvm.loongarch.lasx.cast.128(<2 x i64>)
- <8 x float> @llvm.loongarch.lasx.concat.128.s(<4 x float>, <4 x
float>)
- <4 x double> @llvm.loongarch.lasx.concat.128.d(<2 x double>, <2 x
double>)
- <4 x i64> @llvm.loongarch.lasx.concat.128(<2 x i64>, <2 x i64>)
- <4 x float> @llvm.loongarch.lasx.extract.128.lo.s(<8 x float>)
- <2 x double> @llvm.loongarch.lasx.extract.128.lo.d(<4 x double>)
- <2 x i64> @llvm.loongarch.lasx.extract.128.lo(<4 x i64>)
- <4 x float> @llvm.loongarch.lasx.extract.128.hi.s(<8 x float>)
- <2 x double> @llvm.loongarch.lasx.extract.128.hi.d(<4 x double>)
- <2 x i64> @llvm.loongarch.lasx.extract.128.hi(<4 x i64>)
- <8 x float> @llvm.loongarch.lasx.insert.128.lo.s(<8 x float>, <4 x
float>)
- <4 x double> @llvm.loongarch.lasx.insert.128.lo.d(<4 x double>, <2 x
double>)
- <4 x i64> @llvm.loongarch.lasx.insert.128.lo(<4 x i64>, <2 x i64>)
- <8 x float> @llvm.loongarch.lasx.insert.128.hi.s(<8 x float>, <4 x
float>)
- <4 x double> @llvm.loongarch.lasx.insert.128.hi.d(<4 x double>, <2 x
double>)
- <4 x i64> @llvm.loongarch.lasx.insert.128.hi(<4 x i64>, <2 x i64>)