We shouldn't be using module here.

This is required so that the SITL simulator receives a feedback from
PX4.

This uses the "fake" px4_sem based on mutex and condition_variable on
all POSIX system, not just macOS and Cygwin. This means that we can
change px4_sem_timedwait under the hood and inject the simulated time.

This integrates the lockstep_scheduler, so that the system time is set
by the mavlink HIL_SENSOR message.

This means that the speed factor is removed and the speed is entirely
given by the simulator.

This should be enough for now, especially when we want to raise the
speed of the simulation.

This is just an intermediate step until we can copy the sources over.

These contains some rough changes trying to get SITL to speed up by a
SPEED_FACTOR.

This platform time code probably requires some more thought and refactor
but this gets a demo at 4x working.

This adds the argument -f for a speed factor to speed up the simulation.

This is another step to isolate time from the system.

This is a step towards isolating time from the system.

    - v2.0 in PX4/Firmware (3256e67fdc5e86b5d8c6378ea24ff8a065b65ba8): https://github.com/mavlink/c_library_v2/commit/c38176a0a63556815ea117c6877ce2dd18739231
    - v2.0 current upstream: https://github.com/mavlink/c_library_v2/commit/175ab6725cc0d96827d04ffeeaf3a7797a9abdbf
    - Changes: https://github.com/mavlink/c_library_v2/compare/c38176a0a63556815ea117c6877ce2dd18739231...175ab6725cc0d96827d04ffeeaf3a7797a9abdbf

    175ab67 2018-12-17 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/eaa914c7d9789bc37c9a6a59a5bd1171634bd429
4d5fa0d 2018-12-14 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/48df7ea08abb5d87df6ccb1f9a69b91ff3b89c7a
b65cfcd 2018-12-14 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/b671d3c24d5fc6aa964cd07a4a46566d4dbd7862
8473fe2 2018-12-13 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/2b9d470011a0d62fbfc3183ee172201e5170f7af
5a186d4 2018-12-13 PX4BuildBot - autogenerated headers for rev https://github.com/mavlink/mavlink/tree/68ed09da2e341b2932d9c9d761d7baa811191dc2

    - matrix in PX4/Firmware (3e5d66580520e5ae64555c5fc9252c6c661389e3): https://github.com/PX4/Matrix/commit/9c0acfba36a928b7b002eea3a9dca54a5a0c1250
    - matrix current upstream: https://github.com/PX4/Matrix/commit/18fba8221cc1840964c43f04d8c2aa21857e1b9b
    - Changes: https://github.com/PX4/Matrix/compare/9c0acfba36a928b7b002eea3a9dca54a5a0c1250...18fba8221cc1840964c43f04d8c2aa21857e1b9b

    18fba82 2018-12-16 Matthias Grob - quaternion: improve comments
a4f39c0 2018-12-16 Matthias Grob - quaternion: reuse existing dot product

* the bearing difference between the waypoints and aircraft to landing point should be wrap_pi'ed

* mavlink_messages: remove LOCAL_POSITION_NED_COV stream

* mavlink_messages.cpp: add ODOMETRY stream

* add MAV_ODOM_LP parameter to activate odometry loopback

* EKF2: add vehicle_odometry publisher

* Replace VISION_POSITION_ESTIMATE loopback with ODOMETRY

* LPE: add vehicle_odometry publisher

* set vehicle_odometry local_frame field

* mavlink_messages.cpp: ODOMETRY frame_id depends on MAV_ODOM_LP

These files are copied by accident and then discovered by shellcheck.

Shellcheck complained about returning -1 because that's essentially 255.

This was required for shellsheck.

The startup file rc.board is copied to the build/../genromfs folder
after the pruning of the files happened. Thus, about 2000 bytes of
comments and whitespace were included in the ROMFS.

This commit moves pruning of the files in ROMFS to a separate cmake
custom command which happens after the ROMFS files have been copied and
the extra files have been added.

Testing showed that this change only affected the rc.board file as
expected.