enviornment/llvm-prefix: add Toolchain interface

src/environment/llvm-prefix.ts

@@ -1,5 +1,22 @@
 import path from "path";
 
+export interface Toolchain {
+    /**
+     * C compiler.
+     */
+    CC: string;
+
+    /**
+     * C++ compiler.
+     */
+    CXX: string;
+
+    /**
+     * Fortran compiler.
+     */
+    FC: string;
+};
+
 export function llvmToolchain(prefix: string) {
     const bin = path.resolve(prefix, "bin");
     return {