use ROC_ZIG environment variable to configure which zig is used

compiler/test_gen/src/helpers/llvm.rs

@@ -369,7 +369,7 @@ pub fn helper_wasm<'a>(
 
     use std::process::Command;
 
-    Command::new("zig")
+    Command::new(&crate::helpers::zig_executable())
         .current_dir(dir_path)
         .args(&[
             "wasm-ld",

compiler/test_gen/src/helpers/mod.rs

@@ -10,6 +10,13 @@ pub mod wasm;
 #[cfg(feature = "gen-wasm")]
 pub mod wasm32_test_result;
 
+pub fn zig_executable() -> String {
+    match std::env::var("ROC_ZIG") {
+        Ok(path) => path,
+        Err(_) => "zig".into(),
+    }
+}
+
 /// Used in the with_larger_debug_stack() function, for tests that otherwise
 /// run out of stack space in debug builds (but don't in --release builds)
 #[allow(dead_code)]

compiler/test_gen/src/helpers/wasm.rs

@@ -188,7 +188,7 @@ pub fn helper_wasm<'a, T: Wasm32TestResult>(
             "#UserApp_main_1",
         ];
 
-        let linker_output = std::process::Command::new("zig")
+        let linker_output = std::process::Command::new(&crate::helpers::zig_executable())
             .args(args)
             .output()
             .unwrap();