Fix CI when codegen .so is clobbered

The workspace builds rustc_codegen_nvvm as a normal Cargo member. During every CUDA build script, cuda_builder re-builds that same crate through -Zcodegen-backend=. Cargo produces two identical librustc_codegen_nvvm.so.

Add a feature to differentiate the two cases, cribbing from rust-gpu as it has the same structure but no overlapping .so issue

Author: LegNeato

Cargo.toml

@@ -31,4 +31,4 @@ opt-level = 3
 
 [workspace.dependencies]
 cuda_std = { path = "crates/cuda_std" }
-cuda_builder = { path = "crates/cuda_builder" }
+cuda_builder = { path = "crates/cuda_builder", version = "=0.3.0", default-features = false }

crates/cuda_builder/Cargo.toml

@@ -8,8 +8,17 @@ description = "Builder for easily building rustc_codegen_nvvm crates"
 repository = "https://github.com/Rust-GPU/rust-cuda"
 readme = "../../README.md"
 
+[package.metadata.docs.rs]
+no-default-features = true
+
+[features]
+default = []
+# HACK(see rust-gpu/spirv-builder): use `dep:` to avoid Cargo auto-creating a feature
+# with the dependency name. Consumers must explicitly opt-in to compiling the backend.
+rustc_codegen_nvvm = ["dep:rustc_codegen_nvvm"]
+
 [dependencies]
-rustc_codegen_nvvm = { version = "0.3", path = "../rustc_codegen_nvvm" }
+rustc_codegen_nvvm = { version = "0.3", path = "../rustc_codegen_nvvm", optional = true }
 nvvm = { path = "../nvvm", version = "0.1" }
 serde = { version = "1.0.217", features = ["derive"] }
 serde_json = "1.0.138"