Having `x11` be a disabler on Windows disables the libpidgin library,
but there are a lot of benefits to it being a disabler in other places.
Instead, just drop the dependency from libpidgin when unavailable.
# UPDATING VERSION NUMBERS FOR RELEASES
#
# The version number is:
# <major>.<minor>.<micro><suffix>
#
# micro += 1
#
# If any functions have been added to libpurple, Pidgin, or Finch:
# micro = 0
# minor += 1
#
# If backwards compatibility has been broken in libpurple, Pidgin, or Finch:
# micro = 0
# minor = 0
# major += 1
# purple_soversion += 1
#
# suffix should be similar to one of the following: