include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/core/signal.h b/include/osmocom/core/signal.h
index 19a2688..6f56496 100644
--- a/include/osmocom/core/signal.h
+++ b/include/osmocom/core/signal.h
@@ -1,5 +1,4 @@
-#ifndef OSMO_SIGNAL_H
-#define OSMO_SIGNAL_H
+#pragma once
 
 #include <stdint.h>
 
@@ -43,5 +42,3 @@
 void osmo_signal_dispatch(unsigned int subsys, unsigned int signal, void *signal_data);
 
 /*! @} */
-
-#endif /* OSMO_SIGNAL_H */