waf: stop build if OSD libs missing and requested

Tools/ardupilotwaf/cxx_checks.py

@@ -233,6 +233,7 @@ def check_SFML(cfg, env):
     for lib in libs:
         if not cfg.check(compiler='cxx', lib=lib, mandatory=False,
                          global_define=True):
+            cfg.fatal("Missing SFML libraries - please install libsfml-dev")
             return False
     
     # see if we need Graphics.hpp or Graphics.h
@@ -241,6 +242,7 @@ def check_SFML(cfg, env):
                      msg="Checking for Graphics.hpp", mandatory=False):
         if not cfg.check(compiler='cxx', fragment='''#include <SFML/Graphics.h>\nint main() {}''', define_name="HAVE_SFML_GRAPHICS_H",
                          msg="Checking for Graphics.h", mandatory=False):
+            cfg.fatal("Missing SFML headers SFML/Graphics.hpp or SFML/Graphics.h")
             return False
     env.LIB += libs
     return True