Fix headerguards and clarify endifs

require-ess/src/asprintf.h

-#ifndef asprintf_h
-#define asprintf_h
+#pragma once
+
 #ifdef __cplusplus
 extern "C" {
-#endif
+#endif // __cplusplus
+
 #include <stdarg.h>
+
 #ifndef __GNUC__
 #define __attribute__(arg)
-#endif
+#endif // __GNUC__
 
 int asprintf(char **pbuffer, const char *format, ...)
     __attribute__((__format__(__printf__, 2, 3)));
 int vasprintf(char **pbuffer, const char *format, va_list ap)
     __attribute__((__format__(__printf__, 2, 0)));
+
 #ifdef __cplusplus
 }
-#endif
-#endif
+#endif // __cplusplus

require-ess/src/dbLoadTemplate.h

@@ -6,13 +6,10 @@
 * EPICS BASE is distributed subject to a Software License Agreement found
 * in file LICENSE that is included with this distribution.
 \*************************************************************************/
-/* dbLoadTemplate.h */
 
-#ifndef INCdbLoadTemplateh
-#define INCdbLoadTemplateh
+#pragma once
 
 #include "dbCoreAPI.h"
+
 DBCORE_API int dbLoadTemplate(const char *sub_file, const char *cmd_collect,
                               const char *path);
-
-#endif /*INCdbLoadTemplateh*/

require-ess/src/expr.h

-#ifndef expr_h
-#define expr_h
+#pragma once
 
 #include <stddef.h>
 
 #ifdef __cplusplus
 extern {
-#endif
+#endif // __cplusplus
 
   extern int exprDebug;
 
@@ -20,5 +19,4 @@ extern {
 
 #ifdef __cplusplus
 }
-#endif
-#endif
+#endif // __cplusplus

require-ess/src/require.h

-#ifndef require_h
-#define require_h
+#pragma once
 
 #ifdef __cplusplus
 extern "C" {
-#endif
+#endif // __cplusplus
 
 #ifndef __GNUC__
 #define __attribute__(dummy)
-#endif
+#endif // __GNUC__
 
 int require(const char *libname, const char *version, const char *args);
 size_t foreachLoadedLib(size_t (*func)(const char *name, const char *version,
@@ -23,6 +22,4 @@ void pathAdd(const char *varname, const char *dirname);
 
 #ifdef __cplusplus
 }
-#endif
-
-#endif
+#endif // __cplusplus

require-ess/src/strdup.h

-#ifndef strdup_h
-#define strdup_h
+#pragma once
 
 #include <stddef.h>
 
 #ifdef __cplusplus
 extern "C" {
-#endif
+#endif // __cplusplus
+
 char *strdup(const char *s);
 char *strndup(const char *s, size_t n);
+
 #ifdef __cplusplus
 }
-#endif
-#endif
+#endif // __cplusplus

require-ess/src/version.h

+#pragma once
+
 typedef struct semver_t {
   char *version_str;
   int major;