trace: [stderr] add support for dynamically enabling/disabling events

Uses the generic interface provided in "trace/control.h" in order to provide
a programmatic interface as well as command line and monitor controls.

Signed-off-by: Fabien Chouteau <chouteau@adacore.com>
Signed-off-by: Lluís Vilanova <vilanova@ac.upc.edu>
diff --git a/configure b/configure
index 4f9b27c..300d34b 100755
--- a/configure
+++ b/configure
@@ -3078,6 +3078,7 @@
 fi
 if test "$trace_backend" = "stderr"; then
   echo "CONFIG_TRACE_STDERR=y" >> $config_host_mak
+  trace_default=no
 fi
 if test "$trace_backend" = "ust"; then
   echo "CONFIG_TRACE_UST=y" >> $config_host_mak