Definition of __m128i in compat/xmmintrin.h doesn't match Clang's emmintrin.h

I might be completely off here so please correct my understanding:

we have this typedef for `__m128i`:

https://github.com/emscripten-core/emscripten/blob/388a83650902250927a8ef80ab9a9c1ae4ad3825/system/include/compat/xmmintrin.h#L24

and `__i32x4` is:

```cpp
typedef int __i32x4 __attribute__((__vector_size__(16), __aligned__(16)));
```
https://github.com/llvm/llvm-project/blob/a92dbadffe4ff81cbae7303b0f3e723e26fa77b1/clang/lib/Headers/wasm_simd128.h#L28

So the base type is int.

But in native header, `__m128i` is defined in `emmintrin.h`:

```cpp
typedef long long __m128i __attribute__((__vector_size__(16), __aligned__(16)));
```

https://github.com/llvm/llvm-project/blob/a92dbadffe4ff81cbae7303b0f3e723e26fa77b1/clang/lib/Headers/emmintrin.h#L16

And the base type here is long long, which doesn't match int.

This cause some problem with porting some native code, e.g. there are macros used in this project:

https://github.com/ermig1979/Simd/blob/master/src/Simd/SimdConst.h#L108-L117

to broadcast bytes to the 128-bit register, and it boils down to [bit shifts and setting 2 long long,](
https://github.com/ermig1979/Simd/blob/7b2e0afc53c76cc1e26cb446786ceb4a520e1ff5/src/Simd/SimdInit.h#L61) which then causes a problem:

```
src/Simd/SimdConst.h:110:31: error: constant expression evaluates to 217020518514230019 which cannot be narrowed to type 'int' [-Wc++11-narrowing]
const __m128i K8_03 = SIMD_MM_SET1_EPI8(0x03);
```

I guess I can work around this, but just curious about this difference in the typedefs (should we have `typedef __i64x2 __m128i;` instead?

@juj @tlively