Add a top-level make target to rebuild all sysent files.

The sysent target is useful when changing makesyscalls.sh, when
making paired changes to syscalls.master files, or in a future where
freebsd32 sysent entries are built from the default syscalls.master.

Reviewed by:	bdrewery
Obtained from:	CheriBSD
Sponsored by:	DARPA, AFRL
Differential Revision:	https://reviews.freebsd.org/D17899

Makefile

@@ -33,6 +33,7 @@
 # targets             - Print a list of supported TARGET/TARGET_ARCH pairs
 #                       for world and kernel targets.
 # toolchains          - Build a toolchain for all world and kernel targets.
+# sysent              - (Re)build syscall entries from syscalls.master.
 # xdev                - xdev-build + xdev-install for the architecture
 #                       specified with TARGET and TARGET_ARCH.
 # xdev-build          - Build cross-development tools.
@@ -135,6 +136,7 @@ TGTS=	all all-man buildenv buildenvvars buildkernel buildworld \
 	reinstallkernel reinstallkernel.debug \
 	installworld kernel-toolchain libraries maninstall \
 	obj objlink showconfig tags toolchain update \
+	sysent \
 	_worldtmp _legacy _bootstrap-tools _cleanobj _obj \
 	_build-tools _build-metadata _cross-tools _includes _libraries \
 	build32 distribute32 install32 buildsoft distributesoft installsoft \

Makefile.inc1

@@ -1434,6 +1434,18 @@ packageworld: .PHONY
 . endif
 .endfor
 
+_sysent_dirs=	sys/kern
+_sysent_dirs+=	sys/compat/freebsd32
+_sysent_dirs+=	sys/i386/ibcs2
+_sysent_dirs+=	sys/amd64/linux		\
+		sys/amd64/linux32	\
+		sys/arm64/linux		\
+		sys/i386/linux
+sysent: .PHONY
+.for _dir in ${_sysent_dirs}
+	${_+_}${MAKE} -C ${.CURDIR}/${_dir} sysent
+.endfor
+
 #
 # reinstall
 #