Fix the clang-cl self-host build by defining ~DwarfDebug out of line

DwarfDebug.h has a SmallVector member containing a unique_ptr of an
incomplete type.  MSVC doesn't have key functions, so the vtable and
dtor are emitted in AsmPrinter.cpp, where DwarfDebug's ctor is called.
AsmPrinter.cpp include DwarfUnit.h and doesn't get a complete definition
of DwarfTypeUnit.  We could fix the problem by including DwarfUnit.h in
DwarfDebug.h, but that would increase header bloat.  Instead, define
~DwarfDebug out of line.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207701 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/AsmPrinter/DwarfDebug.cpp

@@ -218,6 +218,9 @@ DwarfDebug::DwarfDebug(AsmPrinter *A, Module *M)
   }
 }
 
+// Define out of line so we don't have to include DwarfUnit.h in DwarfDebug.h.
+DwarfDebug::~DwarfDebug() { }
+
 // Switch to the specified MCSection and emit an assembler
 // temporary label to it if SymbolStem is specified.
 static MCSymbol *emitSectionSym(AsmPrinter *Asm, const MCSection *Section,

lib/CodeGen/AsmPrinter/DwarfDebug.h

@@ -557,6 +557,8 @@ class DwarfDebug : public AsmPrinterHandler {
   //
   DwarfDebug(AsmPrinter *A, Module *M);
 
+  ~DwarfDebug() override;
+
   void insertDIE(const MDNode *TypeMD, DIE *Die) {
     MDTypeNodeToDieMap.insert(std::make_pair(TypeMD, Die));
   }