Crystal play exits if trying a demo using C-binding

[hugopl]

Tested with crystal play on v0.34 (archlinux)

Using the following code on crystal play make it crash due to a link error

lib Whatever
  fun crash
end

Whatever.crash

$ crystal play
Listening on http://127.0.0.1:8080
/usr/bin/ld: _main.o: in function `__crystal_main':
./play:5: undefined reference to `crash'
collect2: error: ld returned 1 exit status
Error: execution of command failed with code: 1: `cc "${@}" -o '/home/hugo/.cache/crystal/crystal-run-play-1-7.tmp'  -rdynamic  -lz `command -v pkg-config > /dev/null && pkg-config --libs --silence-errors libssl || printf %s '-lssl -lcrypto'` `command -v pkg-config > /dev/null && pkg-config --libs --silence-errors libcrypto || printf %s '-lcrypto'` -lpcre -lm -lgc -lpthread /usr/lib/crystal/ext/libcrystal.a -levent -lrt -ldl -L/usr/lib -L/usr/local/lib`

IMO it shouldn't crash, but just catch the link error and show to the user. Besides of showing the type information on side panel, etc.. since the code was compiled, just not linked.