[compiler-rt] [scudo] Don't preserve space for regions at init() (DO NOT MERGE) (PR #74531)

[via llvm-commits]

================
@@ -982,6 +999,21 @@ template <typename Config> class SizeClassAllocator64 {
     const uptr Size = getSizeByClassId(ClassId);
     const u16 MaxCount = CacheT::getMaxCached(Size);
 
+    MemMapT &RegionMemMap = Region->MemMapInfo.MemMap;
+    if (UNLIKELY(!RegionMemMap.isAllocated())) {
+      DCHECK_EQ(Region->RegionBeg, 0U);
+      ReservedMemoryT ReservedMemory;
+      ReservedMemory.create(/*Addr=*/0U, RegionSize, "scudo:primary_reserve");
----------------
ChiaHungDuan wrote:

Done. BTW, I did `push -f` to avoid having to cherry-pick all fix-ups. 

https://github.com/llvm/llvm-project/pull/74531