Remove WaitForSanitizers from ptrace monitor & add to global forkserver

This makes should ensure global forkserver will be single threaded before forking the sandboxees as it does not go through WaitAndFork.

Waiting for sanitizers is not needed in the monitor and should reduce latency
by 1 second for all sanitizer builds. Currently it'll always wait up to 1 seconds for the process to become single-threaded, which will never happen as monitor itself is running in a separate thread.

PiperOrigin-RevId: 530878018
Change-Id: Ie9f663848502f2738721861b0ba2dc6f3cc9f1c9

sandboxed_api/sandbox2/forkserver_bin.cc

@@ -63,6 +63,7 @@ int main(int argc, char* argv[]) {
 
   sandbox2::Comms comms(sandbox2::Comms::kDefaultConnection);
   sandbox2::ForkServer fork_server(&comms);
+  sandbox2::sanitizer::WaitForSanitizer();
 
   while (!fork_server.IsTerminated()) {
     pid_t child_pid = fork_server.ServeRequest();

sandboxed_api/sandbox2/monitor_ptrace.cc

@@ -487,8 +487,6 @@ bool PtraceMonitor::InitSetupSignals() {
 }
 
 bool PtraceMonitor::InitPtraceAttach() {
-  sanitizer::WaitForSanitizer();
-
   if (process_.init_pid > 0) {
     if (ptrace(PTRACE_SEIZE, process_.init_pid, 0, PTRACE_O_EXITKILL) != 0) {
       if (errno != ESRCH) {