test/msan/sigwait: Don't silently ignore assertion failures

[guiand]

Summary

As the parent process would return 0 independent of whether the child succeeded, assertions in the child would be ignored.

[eugenis]

LGTM with nit

compiler-rt/test/msan/sigwait.cpp

25

_exit(!WIFEXITED(child_stat))

[guiand]

Changed to use WIFEXITED

compiler-rt/test/msan/sigwait.cpp

 // RUN: %clangxx_msan -std=c++11 -O0 -g %s -o %t && %run %t
 // RUN: %clangxx_msan -DPOSITIVE -std=c++11 -O0 -g %s -o %t && not %run %t 2>&1 | FileCheck %s
 
 #include <assert.h>
 #include <signal.h>
 #include <sys/time.h>
+#include <sys/wait.h>
 #include <unistd.h>
 
 #include <sanitizer/msan_interface.h>
 
 void test_sigwait() {
   sigset_t s;
 #ifndef POSITIVE
   sigemptyset(&s);
   sigaddset(&s, SIGUSR1);
 #endif
   sigprocmask(SIG_BLOCK, &s, 0);
   // CHECK:  MemorySanitizer: use-of-uninitialized-value
 
   if (pid_t pid = fork()) {
     kill(pid, SIGUSR1);
-    _exit(0);
+    int child_stat;
+    wait(&child_stat);
+    _exit(child_stat);
   } else {
     int sig;
     int res = sigwait(&s, &sig);
     assert(!res);
     // The following checks that sig is initialized.
     assert(sig == SIGUSR1);
   }
 }
 
 int main(void) {
   test_sigwait();
   return 0;
 }