fix: Expose CUDA primitives (#2179)

When building autoprecompile chips in GPU in `powdr-labs/powdr`, we need
access to `histogram.cuh` in `openvm/circuit-primitives` to modify
counts of periphery chips. This requires exporting include dir in
`openvm/circuit-primitives` for downstream crates (`powdr-openvm`). We
believe this (and potentially other crates) to be general client
extension usage.

The way we export `openvm/circuit-primitives` to
`powdr-labs/powdr-openvm` is EXACTLY the same as how
`stark-backend/cuda-common` is exported to `openvm`:
-
https://github.com/openvm-org/stark-backend/blob/main/crates/cuda-common/build.rs#L18-L19
-
https://github.com/openvm-org/stark-backend/blob/main/crates/cuda-common/Cargo.toml#L7

---------

Co-authored-by: Schaeff <[email protected]>

Author: qwang98

crates/circuits/primitives/Cargo.toml

@@ -7,6 +7,7 @@ edition.workspace = true
 homepage.workspace = true
 repository.workspace = true
 license.workspace = true
+links = "circuit-primitives-cuda"
 
 [dependencies]
 openvm-stark-backend = { workspace = true }

crates/circuits/primitives/build.rs

@@ -1,3 +1,6 @@
+#[cfg(feature = "cuda")]
+use std::{env, path::PathBuf};
+
 #[cfg(feature = "cuda")]
 use openvm_cuda_builder::{cuda_available, CudaBuilder};
 
@@ -17,5 +20,11 @@ fn main() {
 
         builder.emit_link_directives();
         builder.build();
+
+        // Export include dir for downstream crates:
+        let include_path = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap())
+            .join("cuda")
+            .join("include");
+        println!("cargo:include={}", include_path.display()); // -> DEP_CIRCUIT_PRIMITIVES_CUDA_INCLUDE
     }
 }