Fix lifetime of ClingMMapper

The ClingMMapper must remain available until all ClingMemoryManagers
are destructed, which is typically during shutdown of IncrementalJIT.
This was not the case for the global object MMapperInstance that was
introduced during the upgrade to LLVM 13 because libCling variables
are destructed before running TROOT atexit handlers that shut down
the JIT. In practice, it happened to work but this will change with
the upgrade to LLVM 18 where we see crashes in some tests, potentially
because of upstream commit
llvm/llvm-project@47f5c54

See also commits e0f6c04660 ("Prevent static destruction from ending
DefaultMMapper too early") and 80c14bb948 ("Extend lifetime of
SectionMemoryManager::DefaultMMapper, again") for the same problem
that we previously patched in our copy of LLVM.

lib/Interpreter/IncrementalJIT.cpp

@@ -70,8 +70,6 @@ namespace {
     }
   };
 
-  ClingMMapper MMapperInstance;
-
   // A memory manager for Cling that reserves memory for code and data sections
   // to keep them contiguous for the emission of one module. This is required
   // for working exception handling support since one .eh_frame section will
@@ -133,7 +131,7 @@ namespace {
     AllocInfo m_RWData;
 
   public:
-    ClingMemoryManager() : Super(&MMapperInstance) {}
+    ClingMemoryManager(ClingMMapper& MMapper) : Super(&MMapper) {}
 
     uint8_t* allocateCodeSection(uintptr_t Size, unsigned Alignment,
                                  unsigned SectionID,
@@ -474,7 +472,10 @@ IncrementalJIT::IncrementalJIT(
       return ObjLinkingLayer;
     }
 
-    auto GetMemMgr = []() { return std::make_unique<ClingMemoryManager>(); };
+    auto MMapper = std::make_unique<ClingMMapper>();
+    auto GetMemMgr = [MMapper = std::move(MMapper)]() {
+      return std::make_unique<ClingMemoryManager>(*MMapper);
+    };
     auto Layer =
         std::make_unique<RTDyldObjectLinkingLayer>(ES, std::move(GetMemMgr));