gdb: make-target-delegates.py: make one string raw

Fixes the following flake8 warning:

  make-target-delegates.py:36:39: W605 invalid escape sequence '\s'

Change-Id: I25eeb296f55765e17e5217a2d1e49018f63a3acd
Reviewed-By: Tom Tromey <tom@tromey.com>
Reviewed-By: Andrew Burgess <aburgess@redhat.com>