[dwarfgen] Fix initialization order error. [NFCI]

This commit fixes the `-Werror=reorder` builds.

Author: Francesco Petrogalli

llvm/unittests/DebugInfo/DWARF/DwarfGenerator.cpp

@@ -376,9 +376,9 @@ void dwarfgen::LineTable::writeProloguePayload(
 //===----------------------------------------------------------------------===//
 
 dwarfgen::Generator::Generator()
-    : MAB(nullptr), MCE(nullptr), MS(nullptr), StringPool(nullptr),
-      TLOF(nullptr), Abbreviations(Allocator), StringOffsetsStartSym(nullptr),
-      Version(0) {}
+    : MAB(nullptr), MCE(nullptr), MS(nullptr), TLOF(nullptr),
+      StringPool(nullptr), Abbreviations(Allocator),
+      StringOffsetsStartSym(nullptr), Version(0) {}
 dwarfgen::Generator::~Generator() = default;
 
 llvm::Expected<std::unique_ptr<dwarfgen::Generator>>