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/lib/IR/AsmWriter.h b/llvm/lib/IR/AsmWriter.h
index aef9c8a..cebfca5 100644
--- a/llvm/lib/IR/AsmWriter.h
+++ b/llvm/lib/IR/AsmWriter.h
@@ -12,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_IR_ASSEMBLYWRITER_H
-#define LLVM_IR_ASSEMBLYWRITER_H
+#ifndef LLVM_LIB_IR_ASMWRITER_H
+#define LLVM_LIB_IR_ASMWRITER_H
 
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/SetVector.h"
@@ -121,4 +121,4 @@
 
 } // namespace llvm
 
-#endif //LLVM_IR_ASMWRITER_H
+#endif