devel/llvm-{cheri,cheriot,morello}: new snapshots

Major changes:

llvm-cheri: merge LLVM 15
llvm-cheriot: switch the fork at github.com/CHERIoT-Platform
llvm-morello: merge LLVM 14

Rework patching and filtering of commands and man pages to better
accomdate version skew between the different ports now that all three
have different bases.

Centralize the addition of ${.CURDIR}/files to EXTRA_PATCHS.