fix apple compatibility library

should permit to build sdrangel also with macOS <10.12

apple/apple_compat.c

@@ -57,10 +57,10 @@ int pthread_barrier_wait(pthread_barrier_t *barrier)
     }
 }
 
+#ifdef _DARWIN_FEATURE_CLOCK_GETTIME
 /**
  * Missing POSIX RealTime/Monotonic Clock
  */
-/*
 #include <mach/mach_time.h>
 
 int clock_gettime(int clk_id, struct timespec *t) {
@@ -74,5 +74,6 @@ int clock_gettime(int clk_id, struct timespec *t) {
     t->tv_nsec = nseconds;
     return 0;
 }
-*/
+#endif
+
 #endif // APPLE Compatibility

qrtplib/CMakeLists.txt

@@ -3,6 +3,7 @@ project(qrtplib)
 set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
 
 set (qrtplib_HEADERS
+    ../apple/apple_compat.h
     rtcpapppacket.h
     rtcpbyepacket.h
     rtcpcompoundpacket.h
@@ -45,6 +46,7 @@ set (qrtplib_HEADERS
     )
 
 set(qrtplib_SOURCES
+    ../apple/apple_compat.c
     rtcpapppacket.cpp
     rtcpbyepacket.cpp
     rtcpcompoundpacket.cpp