Add C API (#5072)

sdk-c/build.rs

@@ -0,0 +1,24 @@
+use std::env;
+use std::fs;
+use std::path::Path;
+
+fn main() {
+    let crate_dir = env::var("CARGO_MANIFEST_DIR").unwrap();
+
+    let out_path = Path::new(&crate_dir);
+    let out_path = out_path.join(Path::new("include"));
+
+    // Ensure `out_path` exists
+    fs::create_dir_all(&out_path).unwrap_or_else(|err| {
+        if err.kind() != std::io::ErrorKind::AlreadyExists {
+            panic!("Unable to create {:#?}: {:?}", out_path, err);
+        }
+    });
+
+    let out_path = out_path.join(Path::new("solana.h"));
+    let out_path = out_path.to_str().unwrap();
+
+    cbindgen::generate(crate_dir)
+        .unwrap()
+        .write_to_file(out_path);
+}