/usr/bin/fakeroot:9:4: syntax error: words that are the concatenation of
a name and a colon produce unspecified results

The relevant part of the script is:

#!/bin/sh

# This script first starts faked (the daemon), and then it will run
# the requested program with fake root privileges.

usage () {
cat - >&2 <<EOF
fakeroot, create a fake root environment.
   usage: fakeroot [-l|--lib fakerootlib] [-f|--faked fakedbin]
                   [-i file] [-s file] [-u|--unknown-is-real]
                   [-b|--fd-base fd] [-h|--help] [-v|--version]
                   [--] [command]
EOF
  exit 1
}

9:4 is "usage:"

I'm not sure what the resolution is here. I think it's a mrsh bug, this
script looks fine to me.

Yes, it's an mrsh bug. The parser seems to have issues with
here-documents inside of brace-groups. The minimal reproducer is:

    {
    cat <<EOF
    hey
    EOF
    }

Fixed in 69713863e96fdcb6640d7985be34d4501317faa0 and
e219bef8eae98846d8f89ead54b6847b876f1f97.