[OpenMP] Fix build of stubs library

[Hahnfeld]

Summary

Both Clang and GCC complained that they cannot initialize a return
object of type 'kmp_proc_bind_t' with an 'int'. While at it, also
fix a warning about missing parentheses thrown by Clang.

[AndreyChurbanov]

LGTM (I'd treat this as NFC :).

[Hahnfeld]

In D65284#1601277, @AndreyChurbanov wrote:

LGTM (I'd treat this as NFC :).

Yes, I agree. I'll change the title when committing.

openmp/runtime/src/kmp_stub.cpp

 }
 void *kmp_aligned_malloc(size_t sz, size_t a) {
   i;
   int err;
   void *res;
 #if KMP_OS_WINDOWS
   res = _aligned_malloc(sz, a);
 #else
-  if (err = posix_memalign(&res, a, sz)) {
+  if ((err = posix_memalign(&res, a, sz))) {
     errno = err; // can be EINVAL or ENOMEM
     res = NULL;
   }
 #endif
   return res;
 }
 void *kmp_calloc(size_t nelem, size_t elsize) {
   i;

 void __kmps_get_schedule(kmp_sched_t *kind, int *modifier) {
   i;
   *kind = __kmps_sched_kind;
   *modifier = __kmps_sched_modifier;
 } // __kmps_get_schedule
 
 kmp_proc_bind_t __kmps_get_proc_bind(void) {
   i;
-  return 0;
+  return proc_bind_false;
 } // __kmps_get_proc_bind
 
 double __kmps_get_wtime(void) {
   // Elapsed wall clock time (in second) from "sometime in the past".
   double wtime = 0.0;
   i;
 #if KMP_OS_WINDOWS
   if (frequency > 0.0) {