fuzz: Pass SystemRoot environment variable to subprocess

See https://docs.python.org/3/library/subprocess.html

Author: hebasto

test/fuzz/test_runner.py

@@ -11,14 +11,15 @@
 import configparser
 import logging
 import os
+import platform
 import random
 import subprocess
 import sys
 
 
 def get_fuzz_env(*, target, source_dir):
     symbolizer = os.environ.get('LLVM_SYMBOLIZER_PATH', "/usr/bin/llvm-symbolizer")
-    return {
+    fuzz_env = {
         'FUZZ': target,
         'UBSAN_OPTIONS':
         f'suppressions={source_dir}/test/sanitizer_suppressions/ubsan:print_stacktrace=1:halt_on_error=1:report_error_type=1',
@@ -27,6 +28,10 @@ def get_fuzz_env(*, target, source_dir):
         'ASAN_SYMBOLIZER_PATH':symbolizer,
         'MSAN_SYMBOLIZER_PATH':symbolizer,
     }
+    if platform.system() == "Windows":
+        # On Windows, `env` option must include valid `SystemRoot`.
+        fuzz_env = {**fuzz_env, 'SystemRoot': os.environ.get('SystemRoot')}
+    return fuzz_env
 
 
 def main():