hg: remove reserved identifiers

Per 7.1.3 paragraph, from C draft:

All identifiers that begin with an underscore and either an uppercase letter or
another underscore are always reserved for any use.

mercurial/bdiff.h

@@ -1,5 +1,5 b''
-#ifndef _HG_BDIFF_H_
-#define _HG_BDIFF_H_
+#ifndef HG_BDIFF_H
+#define HG_BDIFF_H
 
 #include "compat.h"
 

mercurial/bitmanipulation.h

@@ -1,5 +1,5 b''
-#ifndef _HG_BITMANIPULATION_H_
-#define _HG_BITMANIPULATION_H_
+#ifndef HG_BITMANIPULATION_H
+#define HG_BITMANIPULATION_H
 
 #include <string.h>
 

mercurial/compat.h

@@ -1,5 +1,5 b''
-#ifndef _HG_COMPAT_H_
-#define _HG_COMPAT_H_
+#ifndef HG_COMPAT_H
+#define HG_COMPAT_H
 
 #ifdef _WIN32
 #ifdef _MSC_VER

mercurial/mpatch.h

@@ -1,5 +1,5 b''
-#ifndef _HG_MPATCH_H_
-#define _HG_MPATCH_H_
+#ifndef HG_MPATCH_H
+#define HG_MPATCH_H
 
 #define MPATCH_ERR_NO_MEM -3
 #define MPATCH_ERR_CANNOT_BE_DECODED -2