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/Target/PowerPC/PPCISelLowering.h b/llvm/lib/Target/PowerPC/PPCISelLowering.h
index 9deecd0..de8f836 100644
--- a/llvm/lib/Target/PowerPC/PPCISelLowering.h
+++ b/llvm/lib/Target/PowerPC/PPCISelLowering.h
@@ -12,8 +12,8 @@
 //
 //===----------------------------------------------------------------------===//
 
-#ifndef LLVM_TARGET_POWERPC_PPC32ISELLOWERING_H
-#define LLVM_TARGET_POWERPC_PPC32ISELLOWERING_H
+#ifndef LLVM_LIB_TARGET_POWERPC_PPCISELLOWERING_H
+#define LLVM_LIB_TARGET_POWERPC_PPCISELLOWERING_H
 
 #include "PPC.h"
 #include "PPCInstrInfo.h"