Replace $(shell find | sort) with $(sort $(shell find))

Kati's find emulator doesn't understand "| sort", so use use the make
function instead so that we can emulate the find commands.

 before: *kati*: shell time (regen): 1.316989 / 187
 after:  *kati*: shell time (regen): 1.249748 / 184

The time has a lot of variance, the important change is the reduction in
number of shell commands. Kati has other issues with some of these (it
doesn't support find's implicit -a), which is why it only goes down by
3. I'll be fixing Kati separately to handle those cases.

Test: diff out/build-aosp_taimen.ninja before&after
Change-Id: I5c8c2993f01a8a6af84963e903a8a0c186a61e82