retire LINKER_FEATURES filter flag

And build libdl unconditionally.  All supported FreeBSD linkers accept
-F / --filter so there is no need to test for support.

Discussed with:	kib
Sponsored by:	The FreeBSD Foundation

lib/Makefile

@@ -42,7 +42,7 @@ SUBDIR=	${SUBDIR_BOOTSTRAP} \
 	libdevctl \
 	libdevinfo \
 	libdevstat \
-	${_libdl} \
+	libdl \
 	libdwarf \
 	libedit \
 	libelftc \
@@ -193,10 +193,6 @@ _libproc=	libproc
 _librtld_db=	librtld_db
 .endif
 
-.if defined(LINKER_FEATURES) && ${LINKER_FEATURES:Mfilter}
-_libdl=		libdl
-.endif
-
 SUBDIR.${MK_OPENSSL}+=	libmp
 SUBDIR.${MK_PMC}+=	libpmc libpmcstat
 SUBDIR.${MK_RADIUS_SUPPORT}+=	libradius

share/mk/bsd.linker.mk

@@ -86,9 +86,6 @@ ${X_}LINKER_FEATURES=
 ${X_}LINKER_FEATURES+=	build-id
 ${X_}LINKER_FEATURES+=	ifunc
 .endif
-.if ${${X_}LINKER_TYPE} != "lld" || ${${X_}LINKER_VERSION} >= 50000
-${X_}LINKER_FEATURES+=	filter
-.endif
 .if ${${X_}LINKER_TYPE} == "lld" && ${${X_}LINKER_VERSION} >= 60000
 ${X_}LINKER_FEATURES+=	retpoline
 .endif

targets/pseudo/userland/lib/Makefile.depend

@@ -60,6 +60,7 @@ DIRDEPS = \
 	lib/libdevdctl \
 	lib/libdevinfo \
 	lib/libdevstat \
+	lib/libdl \
 	lib/libdwarf \
 	lib/libedit/edit/readline \
 	lib/libelf \
@@ -214,10 +215,6 @@ DIRDEPS+= \
 DIRDEPS+= stand/libsa32
 .endif
 
-.if defined(LINKER_FEATURES) && ${LINKER_FEATURES:Mfilter}
-DIRDEPS+= lib/libdl
-.endif
-
 .if ${MK_NAND} != "no"
 DIRDEPS+= lib/libnandfs
 .endif