Linux: fix for undefined BO in mavlink_main_linux.cpp

if termios.h is included before mathlib.h then BO is undefined.
Since mathlib.h is not needed it was removed but I still don't
know why this error occurs.

Also added -lrt to link flags for clock_gettime

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

makefiles/toolchain_native.mk

@@ -193,7 +193,7 @@ ARCHWARNINGSXX		 = $(ARCHWARNINGS) \
 # pull in *just* libm from the toolchain ... this is grody
 LIBM			:= $(shell $(CC) $(ARCHCPUFLAGS) -print-file-name=libm.a)
 #EXTRA_LIBS		+= $(LIBM) 
-EXTRA_LIBS		+= -pthread -lm 
+EXTRA_LIBS		+= -pthread -lm -lrt
 
 # Flags we pass to the C compiler
 #

src/modules/mavlink/mavlink_main_linux.cpp

@@ -68,7 +68,6 @@
 #include <systemlib/systemlib.h>
 #include <geo/geo.h>
 #include <dataman/dataman.h>
-#include <mathlib/mathlib.h>
 #include <mavlink/mavlink_log.h>
 
 #include <uORB/topics/parameter_update.h>