FindThreads: Simplify conditions for not-in-libc checks

If `CMAKE_HAVE_LIBC_PTHREAD` is true, we also set `Threads_FOUND` to
true, which blocks all the other checks from running.

Modules/FindThreads.cmake

@@ -165,21 +165,21 @@ if(CMAKE_HAVE_PTHREAD_H)
   if(CMAKE_HAVE_LIBC_PTHREAD)
     set(CMAKE_THREAD_LIBS_INIT "")
     set(Threads_FOUND TRUE)
-  else()
-    # Check for -pthread first if enabled. This is the recommended
-    # way, but not backwards compatible as one must also pass -pthread
-    # as compiler flag then.
-    if (THREADS_PREFER_PTHREAD_FLAG)
-      _threads_check_flag_pthread()
-    endif ()
-
-    if(CMAKE_SYSTEM MATCHES "GHS-MULTI")
-      _threads_check_lib(posix pthread_create CMAKE_HAVE_PTHREADS_CREATE)
-    endif()
-    _threads_check_lib(pthreads pthread_create CMAKE_HAVE_PTHREADS_CREATE)
-    _threads_check_lib(pthread  pthread_create CMAKE_HAVE_PTHREAD_CREATE)
   endif()
 
+  # Check for -pthread first if enabled. This is the recommended
+  # way, but not backwards compatible as one must also pass -pthread
+  # as compiler flag then.
+  if (THREADS_PREFER_PTHREAD_FLAG)
+    _threads_check_flag_pthread()
+  endif ()
+
+  if(CMAKE_SYSTEM MATCHES "GHS-MULTI")
+    _threads_check_lib(posix pthread_create CMAKE_HAVE_PTHREADS_CREATE)
+  endif()
+  _threads_check_lib(pthreads pthread_create CMAKE_HAVE_PTHREADS_CREATE)
+  _threads_check_lib(pthread  pthread_create CMAKE_HAVE_PTHREAD_CREATE)
+
   _threads_check_flag_pthread()
 endif()