include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/core/defs.h b/include/osmocom/core/defs.h
index 5ffee04..aebe925 100644
--- a/include/osmocom/core/defs.h
+++ b/include/osmocom/core/defs.h
@@ -1,5 +1,4 @@
-#ifndef OSMOCORE_DEFS_H
-#define OSMOCORE_DEFS_H
+#pragma once
 
 /*! \defgroup utils General-purpose utility functions
  *  @{
@@ -46,5 +45,3 @@
 #undef _OSMO_HAS_ATTRIBUTE_DEPRECATED
 
 /*! @} */
-
-#endif