[build] also fix nps build for fixedwing

conf/firmwares/subsystems/fixedwing/fdm_jsbsim.makefile

@@ -12,9 +12,6 @@ SRC_FIRMWARE=firmwares/fixedwing
 
 SRC_BOARD=boards/$(BOARD)
 
-NPSDIR = $(SIMDIR)/nps
-
-
 nps.ARCHDIR = sim
 
 # include Makefile.nps instead of Makefile.sim
@@ -27,7 +24,7 @@ nps.srcs    += $(fbw_srcs) $(ap_srcs)
 nps.CFLAGS  += -DSITL -DUSE_NPS
 nps.CFLAGS  += $(shell pkg-config glib-2.0 --cflags)
 nps.LDFLAGS += $(shell pkg-config glib-2.0 --libs) -lm -lglibivy $(shell pcre-config --libs) -lgsl -lgslcblas
-nps.CFLAGS  += -I$(NPSDIR) -I$(SRC_FIRMWARE) -I$(SRC_BOARD) -I../simulator -I$(PAPARAZZI_HOME)/conf/simulator/nps
+nps.CFLAGS  += -I$(SRC_FIRMWARE) -I$(SRC_BOARD) -I$(PAPARAZZI_SRC)/sw/simulator/nps -I$(PAPARAZZI_HOME)/conf/simulator/nps
 nps.LDFLAGS += $(shell sdl-config --libs)
 
 # use the paparazzi-jsbsim package if it is installed, otherwise look for JSBsim under /opt/jsbsim
@@ -41,9 +38,14 @@ else
 	nps.LDFLAGS += -L$(JSBSIM_LIB) -lJSBSim
 endif
 
+#
+# add the simulator directory to the make searchpath
+#
+VPATH = $(PAPARAZZI_SRC)/sw/simulator
 
+NPSDIR = nps
 nps.srcs += $(NPSDIR)/nps_main.c                 \
-       $(NPSDIR)/nps_fdm_jsbsim.c                \
+       $(NPSDIR)/nps_fdm_jsbsim.cpp              \
        $(NPSDIR)/nps_random.c                    \
        $(NPSDIR)/nps_sensors.c                   \
        $(NPSDIR)/nps_sensors_utils.c             \