Use remaining arguments as the core file name, joined by spaces

Current Linux kernels do argument splitting after parameter substitution,
so a binary with spaces in the filename will get extra arguments passed
for each fragment of the binary filename.

Reported-by: Jakub Wilk <jwilk@jwilk.net>
Reported-in: <20190312145043.jxjoj66kqssptolr@jwilk.net>
See-also: https://bugs.debian.org/924398