This script in combination with <(...) can be used to speed up creating
reproductions from command lines that use '@' files to define their inputs.
An example use case:
Consider a swiftc command line that uses the @ symbol.
swiftc @/foo/bar/baz.txt
When this is run, the @ command is expanded into a filelist in a temporary
file. This doesn't work with -### since -### outputs the command line with a
temporary file for the filelist, but uses a path to a temporary file that
doesn't exist, e.g.:
swift -frontend -filelist /tmp/tmp.filelist ...
To run this command, you use the at-to-filelist command as follows:
swift -frontend -filelist <(at-to-filelist /foo/bar/baz.txt)
