Fixes issue #2144- Propagate CMAKE_EXPORT_COMPILE_COMMANDS variable

[aliounis]

Propagates variable CMAKE_EXPORT_COMPILE_COMANDS to the cmake subprocess in mission_build.cmake

Checklist (Please check before submitting)

• I reviewed the Contributing Guide.
• [ NA] I signed and emailed the appropriate [Contributor License Agreement] -- Government employee

Describe the contribution
This fixes feature request #2144 which has CMake generate a compilation database for all subprojects/targets, helping editors/IDEs with understanding the full cFS/cFE environment.

Testing performed
Steps taken to test the contribution:

1. Build steps (from root of cFS directory)

    mkdir build
    cd build
    cmake -DCMAKE_EXPORT_COMPILE_COMMANDS:BOOL=TRUE ../cfe

2. Execution steps

    find . -iname "compile_commands.json"
    >>> ./cpu1/default_cpu1/compile_commands.json
    >>> ./compile_commands.json

Expected behavior changes
No impact to behavior of cFE itself. Simply causes an extra file to be created (the compilation database) for cFE/cFS apps when requested by the user.

System(s) tested on

• Hardware: linux server/mac book pro
• OS: RHEL8.6,Ubuntu 20.04
• Versions: dev (main branch)

Additional context
N/A

Third party code
N/A

Contributor Info - All information REQUIRED for consideration of pull request
Andrew Liounis - NASA/GSFC

[jphickey]

I hadn't known about this option, seems to work well for me on CMake 3.22 and seems like a beneficial feature.

That being said, I would like to confirm that this works the same on the oldest version of CMake that we still claim to support (3.5) and may need to tweak the formatting of the commit message but otherwise looks good to me.

[aliounis]

For reference I know it at least works with cmake 3.10 from when we were building things on Ubuntu 18.04. The variable itself was introduced in 3.5, so I don't see why this wouldn't work at 3.5, but I could try it out at some point if you would like.

[aliounis]

I just did check with cmake=3.5 and a fresh cFS bundle (from github) and it works as expected on RHEL8