ardupilotwaf: kill env.py

[tpwrules]

This removes a wart in the build system where environment variables from the hwdef generator were written to a Python Pickle file (not a Python source file as the name suggests) then read back in. This cleans that up to just pass the data directly. Unlike the implication in the source code, it was never really possible to use this file to add custom environment variables as it is unconditionally overwritten every compile. Please see the commits for details.

It also uncovers some more warts (for which fixes will be PRed later)

• The whole load_env_vars thing needs rethinking, it was not optional for a long time and can probably be cleaned up
• There should be no need to rerun the hwdef generator at build time, waf has mechanisms to preserve files

Tested that there is no compiler output change for an arbitrary board for each of ChibiOS, ESP32, and Linux.

[peterbarker]

We should probably set it up again in case we move things around over there.

I don't think it will hurt

[tpwrules]

On the other hand it will immediately explode if that happens so it will be easy to fix but I see your point.

[peterbarker]

I do like the look of this, but we do need someone more familiar with this process to review it.

No-compiler-output-change is pretty compelling....

[tpwrules]

I welcome attempts to break it changing targets and bootloaders and cleaning build dirs and etc. Just so long as it's not also broken in the same way in master :)

[peterbarker]

Board                    AP_Periph  blimp  bootloader  copter  heli  iofirmware  plane  rover  sub
CubeOrange-periph-heavy  *                 *
Durandal                            *      *           *       *                 *      *      *
Hitec-Airspeed           *                 *
KakuteH7-bdshot                     *      *           *       *                 *      *      *
MatekF405                           *      *           *       *                 *      *      *
Pixhawk1-1M-bdshot                  *                  *       *                 *      *      *
SITL_x86_64_linux_gnu               0                  0       0                 0      0      0
f103-QiotekPeriph        *                 *
f303-Universal           *                 *
iomcu                                                                *
revo-mini                           *      *           *       *                 *      *      *
skyviper-v2450                                         *

[tridge]

@tpwrules does this have any impact for multi-target waf builds? eg. "./waf plane copter" or "./waf all"

[peterbarker]

So long as we don't cause any regressions, this is a welcome change!

[tpwrules]

@tpwrules does this have any impact for multi-target waf builds? eg. "./waf plane copter" or "./waf all"

Tested both and all binaries match before and after. Note that we do the latter in CI.