Install pre-compiled files into source tree

[will-v-pi]

This adds an install step in the external projects when USE_PRECOMPILED=false to copy the compiled binaries into the source tree.

This also adds a new action to check that the pre-compiled files have been updated correctly, although I'm not sure if we should add that or not, as the files will change slightly depending on the compiler/SDK used so that action will probably fail quite a lot?

Fixes https://github.com/raspberrypi/picotool/pull/240#discussion_r2129222486

[lurch]

Looks like there are merge conflicts (which are probably what's also causing the CI failure?)

[will-v-pi]

That CI failure is why I'm thinking this change doesn't want to have the check action, as the only change has been in the SDK so we don't really need to update the .elf

The conflict is just because the code for those files has been updated

[lurch]

Hmmm, something that's just occurred to me: if a change was made to a comment in one of the .c files, I guess that might result in no change to the generated ELF file; and the CI checks for that comment-fix PR might fail? :thinking: (but I guess in such a scenario we could just ignore the failing CI and merge anyway?)

[will-v-pi]

Hmmm, something that's just occurred to me: if a change was made to a comment in one of the .c files, I guess that might result in no change to the generated ELF file; and the CI checks for that comment-fix PR might fail? 🤔 (but I guess in such a scenario we could just ignore the failing CI and merge anyway?)

Yeah, that's something to bear in mind, but I think that should be fine