Index: head/share/mk/bsd.mkopt.mk
===================================================================
--- head/share/mk/bsd.mkopt.mk
+++ head/share/mk/bsd.mkopt.mk
@@ -18,6 +18,10 @@
 # after all this processing, allowing this file to be included
 # multiple times with different lists.
 #
+# Other parts of the build system will set BROKEN_OPTIONS to a list
+# of options that are broken on this platform. This will not be unset
+# before returning. Clients are expected to always += this variable.
+#
 # Users should generally define WITH_FOO or WITHOUT_FOO, but the build
 # system should use MK_FOO={yes,no} when it needs to override the
 # user's desires or default behavior.
@@ -58,3 +62,11 @@
 .endif # !defined(MK_${var})
 .endfor
 .undef __DEFAULT_NO_OPTIONS
+
+#
+# MK_* options which are always no, usually because they are
+# unsupported/badly broken on this architecture.
+#
+.for var in ${BROKEN_OPTIONS}
+MK_${var}:=	no
+.endfor
Index: head/sys/conf/kern.opts.mk
===================================================================
--- head/sys/conf/kern.opts.mk
+++ head/sys/conf/kern.opts.mk
@@ -83,6 +83,16 @@
 .undef __DEFAULT_NO_OPTIONS
 
 #
+# MK_* options which are always no, usually because they are
+# unsupported/badly broken on this architecture.
+#
+.for var in ${BROKEN_OPTIONS}
+MK_${var}:=	no
+.endfor
+.undef BROKEN_OPTIONS
+#end of bsd.mkopt.mk expanded inline.
+
+#
 # MK_*_SUPPORT options which default to "yes" unless their corresponding
 # MK_* variable is set to "no".
 #
@@ -104,6 +114,3 @@
 .endif
 .endif
 .endfor
-
-
-