[DebugInfo] Fix some Clang-tidy modernize-use-default and Include What You Use warnings; other minor fixes (NFC).

Per Zachary Turner and Mehdi Amini suggestion to make only post-commit reviews.

llvm-svn: 287838
diff --git a/llvm/lib/DebugInfo/DWARF/DWARFCompileUnit.cpp b/llvm/lib/DebugInfo/DWARF/DWARFCompileUnit.cpp
index 39a7c77..faa51e0 100644
--- a/llvm/lib/DebugInfo/DWARF/DWARFCompileUnit.cpp
+++ b/llvm/lib/DebugInfo/DWARF/DWARFCompileUnit.cpp
@@ -8,6 +8,8 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/DebugInfo/DWARF/DWARFCompileUnit.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugAbbrev.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugInfoEntry.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -29,5 +31,4 @@
 }
 
 // VTable anchor.
-DWARFCompileUnit::~DWARFCompileUnit() {
-}
+DWARFCompileUnit::~DWARFCompileUnit() = default;