Compiler allows to use atomics on bitfields, despite not supporting it

[Devaniti]

This code compiles

struct ColorRGBA {
  uint R : 8;
  uint G : 8;
  uint B : 8;
  uint A : 8;
};

StructuredBuffer<ColorRGBA> testBuffer;

float4 PSMain() : SV_TARGET
{
    InterlockedAdd(testBuffer[0].G, 1);
	return 0.0f;
}

But generates 32 bit atomics

%3 = call i32 @dx.op.atomicBinOp.i32(i32 78, %dx.types.Handle %2, i32 0, i32 0, i32 0, i32 undef, i32 1)  ; AtomicBinOp(handle,atomicOp,offset0,offset1,offset2,newValue)

It should not compile, since there are no instruction that could allow arbitrary bit width atomics

Tested on https://github.com/microsoft/DirectXShaderCompiler/releases/tag/v1.6.2112