Avoid defining HAVE_STRUCT_TIMESPEC at all instead of playing with #undefs which will always be fragile

configure.ac

@@ -208,7 +208,7 @@ then
 else
     AC_CHECK_LIB([pthread], [pthread_create])
 fi
-AC_CHECK_TYPES([struct timespec], 
+AC_CHECK_TYPE([struct timespec], 
 	       AC_DEFINE(STARPU_HAVE_STRUCT_TIMESPEC,[],[struct timespec is defined]),
 	       [], [
 #include <sys/types.h>

include/starpu_util.h

@@ -310,8 +310,6 @@ double starpu_timing_now(void);
 #endif
 #include <time.h>
 #if !defined(_MSC_VER) || defined(BUILDING_STARPU)
-#undef HAVE_CONFIG_H
-#undef HAVE_STRUCT_TIMESPEC
 #include <pthread.h>
 #endif
 #ifndef STARPU_HAVE_STRUCT_TIMESPEC