better debugging of failed formula loading

Closes #21680.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
New formula: emacs-clang-complete-async

emacs-clang-complete-async is an emacs extension to complete C and C++
code, it uses libclang to parse the source code on the fly and provides
completion candidates to auto-complete.

Closes #19449.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
vim: add with-compiledby
imagemagick: add an optional dependency on little-cms2

little-cms is deprecated upstream. little-cms2 is maintained,
produces higher quality output, and runs faster.

This commit preserves the ability to use little-cms if desired,
but as far as I know little-cms2 is always preferred.

Closes #19563.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
ENV: add usage note to ncurses_define
Add opensuse package search
isl: use debian mirror

Closes #21683.
qt, qt5: use X11 path helpers