[SPIR-V] Cannot have short, ushort, uint64_t, int64_t or double spec constant

Description

The compiler issues an error for spec constants whose type is a 16-bit integer, 64-bit integer, or double.
There is no fundamental reason this cannot be done for Vulkan.

Steps to Reproduce

https://godbolt.org/z/Pdx7W4srW

compile command: dxc -spirv -T cs_6_8 -enable-16bit-types t.hlsl

Shader:

// double
[[vk::constant_id(0)]]
const double spec_double = 0.0;
RWStructuredBuffer<double> OutDouble : register(u0, space0);

// short
[[vk::constant_id(1)]]
const int16_t spec_short = 0;
RWStructuredBuffer<int16_t> OutShort : register(u1, space0);

// ushort
[[vk::constant_id(2)]]
const uint16_t spec_ushort = 0;
RWStructuredBuffer<uint16_t> OutUShort : register(u2, space0);

// long
[[vk::constant_id(1)]]
const int64_t spec_long = 0;
RWStructuredBuffer<int64_t> OutLong : register(u1, space0);

// ulong
[[vk::constant_id(2)]]
const uint64_t spec_ulong = 0;
RWStructuredBuffer<uint64_t> OutULong : register(u2, space0);

[numthreads(1,1,1)]
void main(uint GI : SV_GroupIndex) {
  OutDouble[GI] = spec_double;
  OutShort[GI] = spec_short;
  OutUShort[GI] = spec_ushort;
  OutLong[GI] = spec_long;
  OutULong[GI] = spec_ulong;
}

Actual Behavior
Errors saying:

error: unsupported specialization constant type

Environment

• DXC version: latest
• Host Operating System: all

Start by reproducing the issue with the provided HLSL shader, Godbolt link, and dxc -spirv -T cs_6_8 -enable-16bit-types command. Trace the compiler path that reports unsupported specialization constant type for the listed 16-bit, 64-bit, and double types. Done means these specialization constants compile successfully for Vulkan SPIR-V without that error.