pedantic nitpickery: coding style with "FILESEXTRAPATHS:prepend"

  (spoiler: turns out this is fine, but it's non-intuitive)

while checking for any other syntactically incorrect assignments to
FILESEXTRAPATHS, i ran across this in
meta-arm/meta-arm/recipes-kernel/linux:

arm-ffa-transport.inc:FILESEXTRAPATHS:prepend := "${ARMFILESPATHS}"

  "aha," i thought, that's clearly another error as it is missing the
trailing colon. turns out, not so, if you examine the contents of that
directory more closely:

arm-ffa-transport.inc:FILESEXTRAPATHS:prepend := "${ARMFILESPATHS}"
linux-yocto%.bbappend:ARMFILESPATHS := "${THISDIR}/files:"
linux-yocto%.bbappend:FILESEXTRAPATHS:prepend:qemuarm64-secureboot = "${ARMFILESPATHS}"
linux-yocto%.bbappend:FILESEXTRAPATHS:prepend:qemuarm-secureboot = "${ARMFILESPATHS}"
linux-yocto%.bbappend:FILESEXTRAPATHS:prepend:qemuarm64 = "${ARMFILESPATHS}"
linux-yocto%.bbappend:FILESEXTRAPATHS:prepend:qemuarm = "${ARMFILESPATHS}"

because the variable ARMFILESPATHS is defined with the trailing colon
already built in.

  yuck. so while this works, i'm not a big fan of adding delimiters to
the value of variables like this.

rday