morello: Enable the Benchmark ABI for kernel builds.

Add the GENERIC-MORELLO-PURECAP-BENCHMARK{-NODEBUG} configs.

sys/arm64/conf/GENERIC-MORELLO-PURECAP-BENCHMARK

@@ -0,0 +1,24 @@
+#
+# GENERIC-MORELLO-BENCHMARKABI -- Generic kernel configuration file for CheriBSD/Morello benchmark ABI kernel
+#
+# For more information on this file, please read the config(5) manual page,
+# and/or the handbook section on Kernel Configuration Files:
+#
+#    https://www.FreeBSD.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig-config.html
+#
+# The handbook is also available locally in /usr/share/doc/handbook
+# if you've installed the doc distribution, otherwise always see the
+# FreeBSD World Wide Web server (https://www.FreeBSD.org/) for the
+# latest information.
+#
+# An exhaustive list of options and more detailed explanations of the
+# device lines is also present in the ../../conf/NOTES and NOTES files.
+# If you are in doubt as to the purpose or necessity of a line, check first
+# in NOTES.
+#
+
+include "GENERIC-MORELLO-PURECAP"
+
+ident		GENERIC-MORELLO-BENCHMARKABI
+
+machine 	arm64 aarch64cb

sys/arm64/conf/GENERIC-MORELLO-PURECAP-BENCHMARK-NODEBUG

@@ -0,0 +1,4 @@
+include	"GENERIC-MORELLO-BENCHMARKABI"
+include	"../../conf/std.nodebug"
+
+ident	GENERIC-MORELLO-BENCHMARKABI-NODEBUG

sys/conf/kern.mk

@@ -151,7 +151,11 @@ CFLAGS+=	-Xclang -morello-vararg=new -Xclang -morello-bounded-memargs
 .endif
 
 .if ${MACHINE_ARCH:Maarch*c*}
+.if ${MACHINE_ARCH:Maarch*cb}
+CFLAGS+=	-mabi=purecap-benchmark
+.else
 CFLAGS+=	-mabi=purecap
+.endif
 .else
 CFLAGS+=	-mabi=aapcs
 .endif
@@ -353,6 +357,7 @@ CCLDFLAGS+=	-fuse-ld=${LD:[1]:S/^ld.//1W}
 # Set target-specific linker emulation name.
 LD_EMULATION_aarch64=aarch64elf
 LD_EMULATION_aarch64c=aarch64elf
+LD_EMULATION_aarch64cb=aarch64elf
 LD_EMULATION_amd64=elf_x86_64_fbsd
 LD_EMULATION_arm=armelf_fbsd
 LD_EMULATION_armv6=armelf_fbsd