Missed X86 optimization of or to use lea when x < CST and TYPE is u16

https://godbolt.org/z/1K7q748PP

```c
#define TYPE unsigned short
#define N 4
#define CST ((TYPE)1 << N)

#ifdef __clang__
TYPE
src (TYPE x)
{
if (x >= CST)
__builtin_unreachable ();
return x | CST;
}
#else
TYPE
src (TYPE x)
{
if (x >= CST)
__builtin_unreachable ();
return x + CST;
}
#endif
```

Clang with -O2 should produce assembly:

```asm
"src":
lea eax, [rdi+16]
ret
```

Start with the C reproducer in the issue and compile it with Clang at -O2, using the linked Godbolt example to inspect the x86 assembly. Trace the optimization path for the unsigned-short `x | CST` or `x + CST` case and compare it with the expected `lea eax, [rdi+16]`; done means Clang emits that form for the reproducer.

Written by the indexing model from the issue text.