Header guard canonicalization, clang part.

Modifications made by clang-tidy with minor tweaks.

llvm-svn: 215557
diff --git a/clang/include/clang-c/Documentation.h b/clang/include/clang-c/Documentation.h
index ad2da07..89373b1 100644
--- a/clang/include/clang-c/Documentation.h
+++ b/clang/include/clang-c/Documentation.h
@@ -12,8 +12,8 @@
 |*                                                                            *|
 \*===----------------------------------------------------------------------===*/
 
-#ifndef CLANG_C_DOCUMENTATION_H
-#define CLANG_C_DOCUMENTATION_H
+#ifndef LLVM_CLANG_C_DOCUMENTATION_H
+#define LLVM_CLANG_C_DOCUMENTATION_H
 
 #include "clang-c/Index.h"