Migrate from #ifndef guards to #pragma once

Using a pragma instead of guards is easier to write, less error prone
and avoids name clashes (a source of very subtle bugs). This pragma
is supported on almost all compilers, including all the compilers we
care about: https://en.wikipedia.org/wiki/Pragma_once#Portability.

This patch does not change the autogenerated files: asn1/asn1c/*.h.

Reviewed-By: Martin Basti <mbasti@redhat.com>
Reviewed-By: Christian Heimes <cheimes@redhat.com>

util/ipa_pwd.h

@@ -20,8 +20,7 @@
  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  */
 
-#ifndef _IPA_PWD_H_
-#define _IPA_PWD_H_
+#pragma once
 
 /* 90 days default pwd max lifetime */
 #define IPAPWD_DEFAULT_PWDLIFE (90 * 24 *3600)
@@ -75,5 +74,3 @@ int ipapwd_generate_new_history(char *password,
                                 int *new_pwd_hlen);
 
 int encode_nt_key(char *newPasswd, uint8_t *nt_key);
-
-#endif