tools: make code cache and snapshot deterministic

Use a fixed random seed to ensure that the generated sources are
identical across runs.

The final node binary still reseeds itself on start-up so there should
be no security implications caused by predictable random numbers (e.g.,
`Math.random()`, ASLR, the hash seed, etc.)

Fixes: nodejs#29108

tools/code_cache/mkcodecache.cc

@@ -26,6 +26,8 @@ int wmain(int argc, wchar_t* argv[]) {
 int main(int argc, char* argv[]) {
 #endif  // _WIN32
 
+  v8::V8::SetFlagsFromString("--random_seed=42");
+
   if (argc < 2) {
     std::cerr << "Usage: " << argv[0] << " <path/to/output.cc>\n";
     return 1;

tools/snapshot/node_mksnapshot.cc

@@ -19,6 +19,8 @@ int wmain(int argc, wchar_t* argv[]) {
 int main(int argc, char* argv[]) {
 #endif  // _WIN32
 
+  v8::V8::SetFlagsFromString("--random_seed=42");
+
   if (argc < 2) {
     std::cerr << "Usage: " << argv[0] << " <path/to/output.cc>\n";
     return 1;