[openmp] [test] Use omp_testsuite.h instead of directly including pthread.h

[mstorsjo]

Summary

OpenMP tests that use pthread functions include this header instead.
On Unix systems, this header includes pthread.h, while it provides
minimal implementations of the used pthread functions for Windows.

openmp/runtime/test/tasking/bug_nested_proxy_task.c

 // RUN: %libomp-compile-and-run
 // The runtime currently does not get dependency information from GCC.
 // UNSUPPORTED: gcc
 
 // Very flaky on openmp-clang-x86_64-linux-debian.
 // https://bugs.llvm.org/show_bug.cgi?id=45397
 // UNSUPPORTED: linux
 
 #include <stdio.h>
 #include <omp.h>
-#include <pthread.h>
+#include "omp_testsuite.h"
 #include "omp_my_sleep.h"
 
 /*
  With task dependencies one can generate proxy tasks from an explicit task
  being executed by a serial task team. The OpenMP runtime library didn't
  expect that and tries to free the explicit task that is the parent of the
  proxy task still working in background. It therefore has incomplete children
  which triggers a debugging assertion.

openmp/runtime/test/tasking/bug_proxy_task_dep_waiting.c

 // RUN: %libomp-compile-and-run
 // The runtime currently does not get dependency information from GCC.
 // UNSUPPORTED: gcc
 
 // Very flaky on openmp-clang-x86_64-linux-debian.
 // https://bugs.llvm.org/show_bug.cgi?id=45397
 // UNSUPPORTED: linux
 
 #include <stdio.h>
 #include <omp.h>
-#include <pthread.h>
+#include "omp_testsuite.h"
 #include "omp_my_sleep.h"
 
 /*
  An explicit task can have a dependency on a target task. If it is not
  directly satisfied, the runtime should not wait but resume execution.
 */
 
 // Compiler-generated code (emulation)