community/emacs: add dependency on gcc and musl-dev for nativecomp

Both are required for it to work.

To test that emacs does not work without these:

• Install any nativecomp emacs variant.
• Remove musl-dev and gcc if they are installed.
• rm -r ~/emacs.d/eln-cache ~/.config/emacs/eln-cache to remove existing nativecomp cache if emacs was run before.
• emacs -Q -nw to run emacs without config in terminal (neither matter for reproduction, it just starts faster that way).
• Exit emacs afterwards by pressing C-x C-e.

Without both of these libraries error buffer will be shown about missing deps, with details available in async comp buffer that you can switch to by running C-x b *As<TAB><Enter>.