[compiler-rt][Fuchsia] Use map name if provided

[leonardchan]

Summary

Prior to this, any allocations coming from the SizeClassAllocator would just have the vmo name "SizeClassAllocator". This will instead use the string passed to the Map functions if provided which provide slightly more info on what the vmo is used for. That is, is it for region data, metadata, or freearray space.

[phosek]

LGTM

compiler-rt/lib/sanitizer_common/sanitizer_fuchsia.cpp

if (status != ZX_OK) {
     return 0;
   }
   IncreaseTotalMmap(map_size);
   return addr;
 }
 
 uptr ReservedAddressRange::Map(uptr fixed_addr, uptr map_size,
                                const char *name) {
-  return DoMmapFixedOrDie(os_handle_, fixed_addr, map_size, base_, name_,
-                          false);
+  return DoMmapFixedOrDie(os_handle_, fixed_addr, map_size, base_,
+                          name ? name : name_, false);
 }
 
 uptr ReservedAddressRange::MapOrDie(uptr fixed_addr, uptr map_size,
                                     const char *name) {
-  return DoMmapFixedOrDie(os_handle_, fixed_addr, map_size, base_, name_, true);
+  return DoMmapFixedOrDie(os_handle_, fixed_addr, map_size, base_,
+                          name ? name : name_, true);
 }
 
 void UnmapOrDieVmar(void *addr, uptr size, zx_handle_t target_vmar) {
   if (!addr || !size)
     return;
   size = RoundUpTo(size, GetPageSize());
 
   zx_status_t status =