Canonicalize header guards into a common format.

Add header guards to files that were missing guards. Remove #endif comments
as they don't seem common in LLVM (we can easily add them back if we decide
they're useful)

Changes made by clang-tidy with minor tweaks.

llvm-svn: 215558
diff --git a/llvm/utils/TableGen/CodeGenInstruction.h b/llvm/utils/TableGen/CodeGenInstruction.h
index 59a4d21..e0a9044 100644
--- a/llvm/utils/TableGen/CodeGenInstruction.h
+++ b/llvm/utils/TableGen/CodeGenInstruction.h
@@ -11,8 +11,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef CODEGEN_INSTRUCTION_H
-#define CODEGEN_INSTRUCTION_H
+#ifndef LLVM_UTILS_TABLEGEN_CODEGENINSTRUCTION_H
+#define LLVM_UTILS_TABLEGEN_CODEGENINSTRUCTION_H
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/CodeGen/MachineValueType.h"