### Problem description
Typing `--help` causes ImHex to exit without outputting anything.
Diagnostic messages from glib, ASan, other libraries that might have
something important to say, etc. are also suppressed.
### Implementation description
This effectively reverts 7c1e33dde6e55ef6347f3b10868a42f456c2ae6a, which
was partially reverted only on Windows by code that was left commented
out in f114239f51ba68c385e3d46721dd9d97ca4a6c21.
Allowing other libraries to print to stderr may make the output ‘ugly’,
but lots of things print to stderr that are important for figuring out
why something is bugged, like ASan and glib.
### Additional things
