[Migrated] We should replace `rustc_codegen_spirv::linker::test` unit tests with compiletest ones.

Issue automatically imported from old repo: https://github.com/EmbarkStudios/rust-gpu/issues/957
Old labels: t: enhancement,a: test
Originally creatd by eddyb on 2022-11-30T16:58:43Z

The main unique aspect of these tests is they take SPIR-V assembly as an input, not Rust code, e.g.:
https://github.com/EmbarkStudios/rust-gpu/blob/acb05d379982f35e6d4fbd85ff28af3e9876cf4c/crates/rustc_codegen_spirv/src/linker/test.rs#L185-L202

However, we might be able to use module_asm! to feed SPIR-V assembly into the compilation, and compiletest does have the ability to introduce dependencies to link against. The main weirdness we might need to deal with is all the definitions from e.g. core that we don't use, but DCE might be able to clean that up.

(Or we could even use e.g. extern "C" FFI in Rust code to describe such situations without module_asm! at all!)

If we can do this transition, we wouldn't have to deal with weird artificial compiler sessions and e.g.:

• #956

Empieza por crates/rustc_codegen_spirv/src/linker/test.rs, especialmente por las pruebas cercanas a las líneas mencionadas, y revisa la compatibilidad con compiletest y el issue #956. Determina si module_asm!, las dependencias de compiletest o Rust FFI pueden representar las entradas de ensamblado SPIR-V. Se considera terminado cuando las pruebas del linker usan compiletest sin las sesiones artificiales del compilador.