[msan] Add static to some msan allocator functions

[stephan.yichao.zhao]

Summary

This is to help review refactor the allocator code.
So it is easy to see which are the real public interfaces.

compiler-rt/lib/msan/msan_allocator.cpp

if (t) {
     allocator.Deallocate(cache, p);
   } else {
     SpinMutexLock l(&fallback_mutex);
     AllocatorCache *cache = &fallback_allocator_cache;
     allocator.Deallocate(cache, p);
   }
 }
 
-void *MsanReallocate(StackTrace *stack, void *old_p, uptr new_size,
+static void *MsanReallocate(StackTrace *stack, void *old_p, uptr new_size,
                             uptr alignment) {
   Metadata *meta = reinterpret_cast<Metadata*>(allocator.GetMetaData(old_p));
   uptr old_size = meta->requested_size;
   uptr actually_allocated_size = allocator.GetActuallyAllocatedSize(old_p);
   if (new_size <= actually_allocated_size) {
     // We are not reallocating here.
     meta->requested_size = new_size;
     if (new_size > old_size) {
       if (flags()->poison_in_malloc) {
         stack->tag = StackTrace::TAG_ALLOC;
         PoisonMemory((char *)old_p + old_size, new_size - old_size, stack);
       }
     }
     return old_p;
   }
   uptr memcpy_size = Min(new_size, old_size);
   void *new_p = MsanAllocate(stack, new_size, alignment, false /*zeroise*/);
   if (new_p) {
     CopyMemory(new_p, old_p, memcpy_size, stack);
     MsanDeallocate(stack, old_p);
   }
   return new_p;
 }
 
-void *MsanCalloc(StackTrace *stack, uptr nmemb, uptr size) {
+static void *MsanCalloc(StackTrace *stack, uptr nmemb, uptr size) {
   if (UNLIKELY(CheckForCallocOverflow(size, nmemb))) {
     if (AllocatorMayReturnNull())
       return nullptr;
     ReportCallocOverflow(nmemb, size, stack);
   }
   return MsanAllocate(stack, nmemb * size, sizeof(u64), true);
 }