cosmetic: convert explicit warnings to fixme/todo

We do not use this style (#warning as an issue tracker replacement) in
any other Osmocom project. Also those warnings clutter compiler output
making it harder to spot warnings for the actual code.

Change-Id: I72070e2a027e60e8b80c12ccfa23ff075434689f
diff --git a/src/gprs_rlcmac_meas.cpp b/src/gprs_rlcmac_meas.cpp
index d6bbc19..41a7531 100644
--- a/src/gprs_rlcmac_meas.cpp
+++ b/src/gprs_rlcmac_meas.cpp
@@ -28,7 +28,7 @@
 /*
  * downlink measurement
  */
-#warning "TODO: trigger the measurement report from the pollcontroller and use it for flow control"
+/* TODO: trigger the measurement report from the pollcontroller and use it for flow control */
 
 /* received Measurement Report */
 int gprs_rlcmac_meas_rep(Packet_Measurement_Report_t *pmr)