Add sanity check commands to Clang easyblock and print warning for missing ncurses

[Flamefire]

Loading the clang module and trying to run it makes it error with a missing ncurses lib which isn't currently detected.

I added sanity check commands and a warning to avoid this.

Question: Do we want this here and update the ECs or repeat the sanity check commands in every EC to avoid breaking existing ones?

[migueldiascosta]

well, in systems where the existing ECs work because ncurses is installed at the system level, this doesn't break them, so it will only break installations that wouldn't work anyway... I'd say option a...

[Flamefire]

I updated many Clang ECs to include the ncurses dependency.

Note that ncurses is autodetected and as we have cmake as a build dependency for clang it gets detected and used. I guess the issue didn't show because the Clang module was mostly loaded with something else (e.g. CMake) which loads ncurses.

[migueldiascosta]

lgtm

[migueldiascosta]

Going in, thanks @Flamefire!