tsan: ignore some errors in the clone_setns test

[dvyukov]

Summary

Some bots failed with:
unshare failed: 1
https://lab.llvm.org/buildbot/#/builders/70/builds/14101

Look only for the target EINVAL error.

compiler-rt/test/tsan/Linux/clone_setns.cpp

 // RUN: %clangxx_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
 
 // The test models how sandbox2 unshares user namespace after clone:
 // https://github.com/google/sandboxed-api/blob/c95837a6c131fbdf820db352a97d54fcbcbde6c0/sandboxed_api/sandbox2/forkserver.cc#L249
 // which works only in sigle-threaded processes.
 
 #include "../test.h"
 #include <errno.h>
 #include <sched.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 
 static int cloned(void *arg) {
-  if (unshare(CLONE_NEWUSER)) {
+  // Unshare can fail for other reasons, e.g. no permissions,
+  // so check only the error we are interested in:
+  // if the process is multi-threaded unshare must return EINVAL.
+  if (unshare(CLONE_NEWUSER) && errno == EINVAL) {
     fprintf(stderr, "unshare failed: %d\n", errno);
     exit(1);
   }
   exit(0);
   return 0;
 }
 
 int main() {