- explicitly set TOOLCHAIN on all NuttX targets

You can now add `DYNAMIC` as an option to `px4_add_module`, which will
cause that module to no longer be compiled into the px4 executable, but
instead produce a separate shared library file, which can be loaded and
executed with the new `dyn` command:

    pxh> dyn ./hello.px4mod start

This will load the shared object file `hello.px4mod` if it wasn't
already loaded, and execute its main function with the given arguments.

The threads running commands for clients through the Posix daemon used
to write to a char buffer through snprintf (etc.) which was then written
directly to the file descriptor, whereas in the other case printf
(etc.) was used to write to stdout (FILE*). Both versions used some
macro's and repeated code to have the same output.

This change unifies these two cases by using a FILE* in both cases. The
(line) buffering is done by the standard C library's implementation
(just like with stdout), and px4_log.c now uses the same code in all
cases (using fprintf, etc.) for printing (colored) output.

Because it was always failing from the beginning on and
we want to make sure no other tests break in the meantime
by running the currently passing tests also on Windows CI.

This triggered POLLHUP too early on Mac.

Unlike pipes, unix sockets provide bi-directional
communication with each connected client.

- No need to generate a unique uuid per client anymore.

- The client doesn't have to create its own pipe anymore.

- Since there is no risk of multiple client's writes getting mixed up,
  messages don't need to fit in a single write anymore, removing the
  limit on command length.

- Since the server can detect a connection closing, the client no longer
  needs to handle signals. When the client is killed, the connection is
  automatically closed, which will cause the server to kill the related
  px4 thread.
  Since this does not rely on handling signals and the client sending an
  additional message, this is much more reliable.

- Client is no longer a singleton.

- The protocol is simplified. Standard output is directly written to the
  socket back to the client, without wrapping it in any protocol
  message.

- Because of the simple protocol, one could now even use netcat to run a
  px4 command:

    $ echo hello | netcat -UN /tmp/px4-sock-0

Also removes a few race conditions.

Fixes these invalid format strings:
- A `%d` for a pointer (replaced it by `%p`)
- A 0x%08x (and a 0x%0x8!) for a pointer (replaced by %p)
- 2 cases of `%d` for a `ssize_t` (replaced it by `%zi`)
- 1 case of a %u for an `int` (replaced by %i)
- 3 cases of %d for a `long` (replaced by %ld)
- 19 cases of `%d`, `%i`, `%u` or `%lu` for a `size_t` (replaced it by `%zu`)
- An unused formatting argument (removed it)
- A missing `%d` (added it)
- A missing `%s` (added it)
- 2 cases of `%llu` for a `uint64_t` (replaced it by `"%" PRIu64`)
- 6 cases of giving a string directly as format string (replaced it by `("%s", string)`)
- 2 cases of %*-s, which should probably have been %-*s.
  (Looks like NuttX accepts (the invalid) %*-s, but other platforms don't.)
- A %04x for a `uint32_t` (replaced by "%04" PRIx32)

    - nuttx in PX4/Firmware (31767b6b5aeb4293c2991dbfea6b810e34a34149): https://github.com/PX4/NuttX/commit/999c4357a220d9ea271475e74abd5d8ba080be27
    - nuttx current upstream: https://github.com/PX4/NuttX/commit/166d898c70141d7ddb179b5ead1c5ea726574411
    - Changes: https://github.com/PX4/NuttX/compare/999c4357a220d9ea271475e74abd5d8ba080be27...166d898c70141d7ddb179b5ead1c5ea726574411

166d898 2018-10-18 Daniel Agar - [BACKPORT] Merged in dagar/nuttx/pr-stm32_dma_per_spi (pull request #736)
0a5b1cb 2018-10-17 David Sidrane - [BACKPORT] Lampoo-master-spi-flash (pull request #735)

   This common code can be used byt posix based boars to provide
   the board_identity API.

This uses the systems default shell:
- Ubuntu: dash
- Fedora: bash

Since bash is invoked via /bin/sh, it operates in POSIX mode:
  https://tiswww.case.edu/php/chet/bash/POSIX

- remove '# Ignore the expand_aliases command in zshell.'
  Not needed because the shell operates in POSIX mode
- [[ is bashism -> use [
- autostart_files=( $autostart_file_match )
  is not supported in dash, so use 'ls'
- shellcheck runs the dash flavor, since dash is a minimalistic shell.

Tested on dash & bash.

    - nuttx in PX4/Firmware (1adcfeecc20620f02439093afb85f3151b2e8be1): https://github.com/PX4-NuttX/nuttx/commit/e31e94f5bd3cf68b9ed0f010724ac9122730dd21
    - nuttx current upstream: https://github.com/PX4-NuttX/nuttx/commit/7e3c8e10cd92351b905bc8d0e34e69bccd00dfea
    - Changes: https://github.com/PX4-NuttX/nuttx/compare/e31e94f5bd3cf68b9ed0f010724ac9122730dd21...7e3c8e10cd92351b905bc8d0e34e69bccd00dfea

    7e3c8e1 2018-09-21 Gregory Nutt - [BACKPORT] 510b0f7e07 Correct all ARMv7-M architectures.