Source not included with emitNonSemanticShaderDebugSource

If I have a simple shader like

```glsl
#version 450
#extension GL_EXT_shader_8bit_storage: enable
#extension GL_EXT_shader_explicit_arithmetic_types_int8: enable
layout(push_constant) uniform PushConstant {
int8_t x[4];
} data;

void main(){
gl_Position = vec4(float(data.x[0]) * 0.0);
}
```

and run `glslang -gVS` I will see the `OpString` with all the source, but going

```c++
glslang::SpvOptions spv_options;
spv_options.emitNonSemanticShaderDebugSource = true;
glslang::GlslangToSpv(*program.getIntermediate(stage), spirv, &spv_options);
```

I only get

```
%19 = OpString "// OpModuleProcessed client vulkan100
// OpModuleProcessed target-env vulkan1.0
// OpModuleProcessed entry-point main
#line 1
"
```