This PR reapplies https://github.com/llvm/llvm-project/pull/149461
In the original `combineVectorSizedSetCCEquality`, the result of setcc
is being negated by returning setcc with the same cond code, leading to
wrong logic.
For example, with
```llvm
%cmp_16 = call i32 @memcmp(ptr %a, ptr %b, i32 16)
%res = icmp eq i32 %cmp_16, 0
```
the original PR producese all_true and then also compares the result
equal to 0 (using the same SETEQ in the returning setcc), meaning that
semantically, it effectively is calling icmp ne.
Instead, the PR should have use SETNE in the returning setcc, this way,
all true return 1, then it is compared again ne 0, which is equivalent
to icmp eq.
Fixes https://github.com/llvm/llvm-project/issues/149230
Previously, even with simd enabled via `-mattr=+simd128`, the compiler
cannot utilize v128 to optimize loads and setcc of i128, instead
legalizing it to consecutive i64s.
This PR then adds support for setcc of i128 by converting them to
v16i8's anytrue and alltrue; consequently, this benefits memcmp of 16
bytes or more (when simd128 is present).
The check for enabling this optimization is if the comparison operand is
either a load or an integer in i128, with the comparison code being
either `EQ | NE`, without `NoImplicitFloat` function flag.
Inspiration taken from RISCV's isel lowering.
