integration fix: protect include file

The command line to get the error was:
    ./build_oai --eNB -w EXMIMO -c

targets/RT/USER/rt_wrapper.h

@@ -30,7 +30,8 @@
 * \warning This code will be removed when a legacy libc API becomes available.
 */
 
-
+#ifndef _RT_WRAPPER_H_
+#define _RT_WRAPPER_H_
 
 #define _GNU_SOURCE
 #include <time.h>
@@ -121,3 +122,4 @@ int sched_getattr(pid_t pid,struct sched_attr *attr,unsigned int size, unsigned
 
 #define gettid() syscall(__NR_gettid) // for gettid
 
+#endif /* _RT_WRAPPER_H_ */