bsd.own.mk: No need for MKSLJIT to be set differently from others.

- Use ?=, not =, so mk.conf setting wins.
- Write out per-architecture tabular settings, not a conditional.
- Add comments for the architectures that look like they should have
  sljit but don't.  (XXX Missing comments about powerpc and mips --
  not sure why, is this because modules don't yet work on those
  architectures, or what?)

Tidying for PR 58103: bpfjit.kmod is not built on aarch64.

share/mk/bsd.own.mk

@@ -1,4 +1,4 @@
-#	$NetBSD: bsd.own.mk,v 1.1365 2024/04/02 22:37:34 riastradh Exp $
+#	$NetBSD: bsd.own.mk,v 1.1366 2024/04/02 22:41:48 riastradh Exp $
 
 # This needs to be before bsd.init.mk
 .if defined(BSD_MK_COMPAT_FILE)
@@ -1336,6 +1336,21 @@ MKLLVMRT.i386=		yes
 MKLLVMRT.aarch64=	yes
 .endif
 
+# Just-in-time compiler for bpf, npf acceleration
+MKSLJIT.aarch64=	yes
+MKSLJIT.i386=		yes
+MKSLJIT.sparc=		yes
+#MKSLJIT.sparc64=	yes	# not suppored in sljit (yet?)
+MKSLJIT.x86_64=		yes
+#MKSLJIT.powerpc=	yes	# XXX
+#MKSLJIT.powerpc64=	yes	# XXX
+#MKSLJIT.mipsel=	yes	# XXX
+#MKSLJIT.mipseb=	yes	# XXX
+#MKSLJIT.mips64el=	yes	# XXX
+#MKSLJIT.mips64eb=	yes	# XXX
+#MKSLJIT.riscv32=	yes	# not until we update sljit
+#MKSLJIT.riscv64=	yes	# not until we update sljit
+
 # compat with old names
 MKDEBUGKERNEL?=${MKKDEBUG:Uno}
 MKDEBUGTOOLS?=${MKTOOLSDEBUG:Uno}
@@ -1391,13 +1406,6 @@ _MKVARS.no= \
 ${var}?=	${${var}.${MACHINE_ARCH}:U${${var}.${MACHINE}:Uno}}
 .endfor
 
-.if ${MACHINE_ARCH} == "aarch64" || \
-    ${MACHINE_ARCH} == "i386"    || \
-    ${MACHINE_ARCH} == "sparc"   || \
-    ${MACHINE_ARCH} == "x86_64"
-MKSLJIT=	yes
-.endif
-
 #
 # Which platforms build the xorg-server drivers (as opposed
 # to just Xnest and Xvfb.)