list_vmd_make_targets and list_cmake_targets

* This allows one to run 'make posix list_vmd_make_targets' and get output like

>make posix list_vmd_make_targets
[...]
-- Build files have been written to:
/usr/src/debian/px4/Firmware/Firmware.git/build_posix_sitl_default
PX4 CONFIG: /usr/src/debian/px4/Firmware/Firmware.git/build_posix_sitl_default
Scanning dependencies of target list_vmd_make_targets
[100%] List of acceptable 'posix_sitl_default' <viewer_model_debugger> targets:
none
none_iris
none_iris_opt_flow
none_tailsitter
[...]
replay_solo_valgrind
replay_typhoon_h480_valgrind
[100%] Built target list_vmd_make_targets

Or, run 'make list_vmd_make_targets' from the build_posix_* directory.

* This adds the list_cmake_targets make target to print all
cmake targets that one can match with PX4_NO_OPTIMIZATION.
PX4_NO_OPTIMIZATION is ignored (do optimization as normal)
when the CONFIG isn't posix_sitl_*.

* Add comment in Makefile on how/where to find all targets.

Makefile

@@ -148,6 +148,9 @@ endef
 # --------------------------------------------------------------------
 #  Do not put any spaces between function arguments.
 
+# For a list of all config targets, please look in cmake/configs,
+# For example: ls cmake/configs | sed -e 's/\.cmake$//'
+
 # All nuttx, posix and qurt targets.
 nuttx_% posix_% qurt_%:
 	$(call cmake-build,$@)
@@ -288,7 +291,7 @@ viewers = gazebo jmavsim replay
 sitl_vmd_triplet_masks = $(foreach viewer,$(viewers),$(viewer) $(viewer)_%)
 # targets handled by PX4_MAKE
 make_targets = install test upload package package_source debug debug_tui debug_ddd debug_io debug_io_tui debug_io_ddd check_weak \
-	run_cmake_config config $(sitl_vmd_triplet_masks)
+	run_cmake_config config list_vmd_make_targets list_cmake_targets $(sitl_vmd_triplet_masks)
 $(foreach targ,$(make_targets),$(eval $(call make-targ,$(targ))))
 
 .PHONY: clean