[asan] Fix macOS FindDynamicShadowStart to consider the last gap in the VM map

[kubamracek]

Summary

It looks FindDynamicShadowStart has a bug: When iterating over the memory map, we will not consider the very last gap in the address space. Let's fix that.

compiler-rt/trunk/lib/sanitizer_common/sanitizer_mac.cc

uptr FindAvailableMemoryRange(uptr shadow_size,
   if (largest_gap_found) *largest_gap_found = 0;
   while (kr == KERN_SUCCESS) {
     mach_vm_size_t vmsize = 0;
     natural_t depth = 0;
     RegionInfo vminfo;
     mach_msg_type_number_t count = kRegionInfoSize;
     kr = mach_vm_region_recurse(mach_task_self(), &address, &vmsize, &depth,
                                 (vm_region_info_t)&vminfo, &count);
+    if (kr == KERN_INVALID_ADDRESS) {
+      // No more regions beyond "address", consider the gap at the end of VM.
+      address = GetMaxVirtualAddress() + 1;
+      vmsize = 0;
+    }
     if (free_begin != address) {
       // We found a free region [free_begin..address-1].
       uptr gap_start = RoundUpTo((uptr)free_begin + left_padding, alignment);
       uptr gap_end = RoundDownTo((uptr)address, alignment);
       uptr gap_size = gap_end > gap_start ? gap_end - gap_start : 0;
       if (shadow_size < gap_size) {
         return gap_start;
       }