wasm2c: allow test script to specify a runner app

This is useful to specify debuggers, launch the tests in qemu emulators for different platforms etc.

Author: shravanrn

test/run-spec-wasm2c.py

@@ -665,7 +665,8 @@ def main(args):
 
             # Run the resulting binary
             if options.run:
-                return subprocess.run([main_exe]).returncode
+                test_runner = os.getenv('WASM2C_TEST_RUNNER', '').split()
+                return subprocess.run(test_runner + [main_exe]).returncode
     return 0