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

llvm-svn: 296404
diff --git a/llvm/lib/CodeGen/GCStrategy.cpp b/llvm/lib/CodeGen/GCStrategy.cpp
index 31ab86f..6be4c16 100644
--- a/llvm/lib/CodeGen/GCStrategy.cpp
+++ b/llvm/lib/CodeGen/GCStrategy.cpp
@@ -1,4 +1,4 @@
-//===-- GCStrategy.cpp - Garbage Collector Description --------------------===//
+//===- GCStrategy.cpp - Garbage Collector Description ---------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
@@ -18,7 +18,4 @@
 
 LLVM_INSTANTIATE_REGISTRY(GCRegistry)
 
-GCStrategy::GCStrategy()
-    : UseStatepoints(false), NeededSafePoints(0), CustomReadBarriers(false),
-      CustomWriteBarriers(false), CustomRoots(false), InitRoots(true),
-      UsesMetadata(false) {}
+GCStrategy::GCStrategy() = default;