Add wait for child process(s) to exit.

[rsundahl]

Summary

It was possible for the parent process to exit before the
forked child process had finished. In some shells, this
causes the pipe to close and FileCheck misses some output
from the child. Waiting for the child process to exit before
exiting the parent, assures that all output from stdout and
stderr is combined and forwarded through the pipe to FileCheck.

rdar://95241490

[yln]

Thanks, I like this attempt to make the test less flaky!

Note that on Linux the compilation of the test file now fails:

/var/lib/buildkite-agent/builds/llvm-project/compiler-rt/test/asan/TestCases/Posix/coverage-fork.cpp:37:11: error: use of undeclared identifier 'wait'
    while(wait(NULL) > 0);

Is there a common header we can include?

[yln]

I think it's: #include <sys/wait.h>

[rsundahl]

Adding include of <sys/wait.h> for Linux.

[rsundahl]

In D128565#3609702, @yln wrote:

I think it's: #include <sys/wait.h>

...and I knew better! Thanks for catching this.

[rsundahl]

Applied clang-format

compiler-rt/test/asan/TestCases/Posix/coverage-fork.cpp

int main(int argc, char **argv) {
   pid_t child_pid = fork();
   if (child_pid == 0) {
     fprintf(stderr, "Child PID: %d\n", getpid());
     baz();
   } else {
     fprintf(stderr, "Parent PID: %d\n", getpid());
     foo();
     bar();
+
+    // Wait for the child process(s) to finish
+    while(wait(NULL) > 0);
   }
   return 0;
 }
 
 // CHECK-DAG: Child PID: [[ChildPID:[0-9]+]]
 // CHECK-DAG: [[ChildPID]].sancov: {{.*}} PCs written
 // CHECK-DAG: Parent PID: [[ParentPID:[0-9]+]]
 // CHECK-DAG: [[ParentPID]].sancov: 3 PCs written