From the SPIR-V Spec 2.16.1:
A function declaration (an OpFunction with no basic blocks), must have
a Linkage Attributes Decoration with the Import Linkage Type.
A function definition (an OpFunction with basic blocks) cannot be
decorated with the Import Linkage Type.
When applied to a structure-type member, all members of that structure
type must also be decorated with BuiltIn. (No allowed mixing of built-in
variables and non-built-in variables within a single structure.)
When applied to a structure-type member, that structure type cannot be
contained as a member of another structure type.
There is at most one object per Storage Class that can contain a
structure type containing members decorated with BuiltIn, consumed per
entry-point.
Added a new file where all the decoration validation can be performed.
In this change the SPIRV Spec Section 2.16.1 is implemented:
"It is illegal to initialize an imported variable. This means
that a module-scope OpVariable with initialization value cannot be
marked with the Import Linkage Type."
Also added unit tests.
