[compiler-rt] [msan] Add 'MappingDesc::ALLOCATOR' type and check it is available (PR #85153)

[Vitaly Buka via llvm-commits]

================
@@ -32,13 +32,13 @@
 struct MappingDesc {
   uptr start;
   uptr end;
-  enum Type {
-    INVALID, APP, SHADOW, ORIGIN
-  } type;
+  enum Type { INVALID, ALLOCATOR, APP, SHADOW, ORIGIN } type;
----------------
vitalybuka wrote:

```suggestion
  enum Type { 
    INVALID = 1,
    ALLOCATOR  =2,
    APP = 4,
    SHADOW = 8,
    ORIGIN = 16,
   } type;
```

https://github.com/llvm/llvm-project/pull/85153