glslc not setting VULKAN = 120, and not compiling to half

How do you

1. Get glslc to set VULKAN define to anything other than 100. I'm requesting 1.2?
2. Get float16_t and f16vec2/3/4 and f16mat2/3/4 to be honored as types?
3. Get functions like clamp(), sign(), abs() to splice in the half version so I don't get a type mismatch error.

Here's the command line to compile. I don't see any other args related to half for the command line. Is no one using half with Vulkan GLSL shaders? I found the following in-depth talk about getting HLSL to generate half, and zero literature on doing the same with GLSL.

And I don't want to use "mediump float" since that often gets mapped to float, and so I need something more explicit. The spirv flags like "--convert-relaxed-to-half " just end up adding a ton of conversions to half with little in the way of perf benefits. If Vulkan really is a mobile API, then half needs to be better supported on iOS and Android and even some consoles.

https://therealmjp.github.io/posts/shader-fp16/

glslc --target-env=vulkan1.2 -fentry-point=main -fauto-bind-uniforms -fauto-map-locations -std=310es testShader.frag -o testShader.spv

```
#version 310 es

//#define VULKAN 120

//#if VULKAN >= 120
// blarg120
//#elseif VULKAN > 110
// blarg110
//#else
// blarg100
//#endif

#if VULKAN >= 120
#extension VK_KHR_shader_float16_int8 : enable
#else
#extension GL_AMD_gpu_shader_half_float: enable
#extension GL_AMD_gpu_shader_half_float_fetch: enable
#endif

#if defined(GL_ES)
precision highp float;
precision highp int;
#endif

// Types defined to closer match Metal and force 16bit ALU
#define half float16_t

half saturate(half x)
{
return clamp(x, half(0.0), half(1.0));
}

layout(location = 0) out vec4 fragColor;

void main()
{
fragColor = vec4(saturate(half(2)));
}
```

Output:
testShader.frag:30: error: 'clamp' : no matching overloaded function found
testShader.frag:30: error: 'return' : type does not match, or is not convertible to, the function's return type