Index: share/mk/bsd.own.mk
===================================================================
--- share/mk/bsd.own.mk	(revision 240466)
+++ share/mk/bsd.own.mk	(working copy)
@@ -432,7 +432,6 @@
     ICONV \
     IDEA \
     INSTALL_AS_USER \
-    LIBCPLUSPLUS \
     NAND \
     OFED \
     SHARED_TOOLCHAIN
@@ -642,6 +641,33 @@
 .endif
 .endfor
 
+#
+# MK_* options that default to on if the compiler is clang.
+#
+.include <bsd.compiler.mk>
+.for var in \
+    LIBCPLUSPLUS
+.if defined(WITH_${var}) && defined(WITHOUT_${var})
+.error WITH_${var} and WITHOUT_${var} can't both be set.
+.endif
+.if defined(MK_${var})
+.error MK_${var} can't be set by a user.
+.endif
+.if ${COMPILER_TYPE} == "clang"
+.if defined(WITHOUT_${var})
+MK_${var}:=	no
+.else
+MK_${var}:=	yes
+.endif
+.else
+.if defined(WITH_${var})
+MK_${var}:=	yes
+.else
+MK_${var}:=	no
+.endif
+.endif
+.endfor
+
 .if ${MK_CTF} != "no"
 CTFCONVERT_CMD=	${CTFCONVERT} ${CTFFLAGS} ${.TARGET}
 .elif defined(MAKE_VERSION) && ${MAKE_VERSION} >= 5201111300