Recognize the VideoCore 4 processor

This is supported in this GCC fork. [1] It has been packaged in Nixpkgs
since 2019. [2]

Their change to `config.sub` [3] is similar, but also includes a `vc4`
-> `vc4-unknown-elf` shorthand; I don't see any reasons to add any new
legacy 1-component short-hands, so I just skipped that part.

[1]: https://github.com/itszor/vc4-toolchain

[2]: https://github.com/NixOS/nixpkgs/pull/72657

[3]: 91278afabe

* config.sub (vc4-*): Recognize.
* testsuite/config-sub.data (vc4-unknown-none-elf): New entry.

Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>

config.sub

@@ -4,7 +4,7 @@
 
 # shellcheck disable=SC2006,SC2268 # see below for rationale
 
-timestamp='2023-10-19'
+timestamp='2023-10-28'
 
 # This file is free software; you can redistribute it and/or modify it
 # under the terms of the GNU General Public License as published by
@@ -1253,6 +1253,7 @@ case $cpu-$vendor in
 			| ubicom32 \
 			| v70 | v850 | v850e | v850e1 | v850es | v850e2 | v850e2v3 \
 			| vax \
+			| vc4 \
 			| visium \
 			| w65 \
 			| wasm32 | wasm64 \

testsuite/config-sub.data

@@ -855,6 +855,7 @@ v850es						v850es-unknown-none
 v850es-elf					v850es-unknown-elf
 vax						vax-dec-ultrix4.2
 vaxv						vax-dec-sysv
+vc4-unknown-none-elf				vc4-unknown-none-elf
 visium						visium-unknown-none
 visium-elf					visium-unknown-elf
 vms						vax-dec-vms