Add the dirlinks target to some Makefiles.  This plugs some wholes open by last chicken-and-egg build fix

apps/canutils/libcanard: Update version

(1) Make.defs set the include path in CFLAGS, but not in CXXFLAGS, (2) canutils/libuavcan/Makefile should not use explication / delimiters.  It should not use -I.  I should use DELIM: command not found and nuttx/tools/incdir.sh

apps/examples/pty_test: If CONFIG_SERIAL_TERMIOS is not selected, then don't call tcgetattr or tcsetattr.

minor; media app is intended to take either a command line argument, or a compiled-in default value from config.  However, the default is ignored, leading to confusing error messages.

minor; media app is intended to take either a command line argument, or a compiled-in default value from config.  However, the default is ignored, leading to confusing error messages.

apps/examples/pty_test:  Use of POLL must be optional. There are still a few character drivers that do not support it.