build: rename $(LIBDL) to $(DL_LIBS) and modify detection

configure.ac

@@ -275,8 +275,8 @@ LT_LIB_M
 dnl
 dnl Checks for libdl - on certain platforms its part of libc
 dnl
-AC_CHECK_LIB([dl], [dladdr], LIBDL="-ldl", LIBDL="")
-AC_SUBST(LIBDL)
+AC_SEARCH_LIBS([dlopen], [dl dld], [], [ac_cv_search_dlopen=])
+AC_SUBST([DL_LIBS], "$ac_cv_search_dlopen")
 
 PKG_CHECK_MODULES(GLIB, [gio-unix-2.0 >= 2.37.6 gmodule-2.0],
 	[AC_SUBST(LOG_DRIVER, '$(top_srcdir)/build-aux/tap-driver.sh')

libnm/Makefile.am

@@ -137,7 +137,7 @@ GLIB_MKENUMS_C_FLAGS = --identifier-prefix NM --fhead '\#include "nm-default.h"\
 libnm_la_LIBADD = \
 	$(top_builddir)/libnm-core/libnm-core.la \
 	$(top_builddir)/introspection/libnmdbus.la \
-	$(LIBDL) \
+	$(DL_LIBS) \
 	$(GLIB_LIBS) \
 	$(UUID_LIBS) \
 	$(GUDEV_LIBS)

src/Makefile.am

@@ -491,7 +491,7 @@ libNetworkManager_la_LIBADD = \
 	$(LIBNL_LIBS) \
 	$(SYSTEMD_LOGIN_LIBS) \
 	$(LIBNDP_LIBS) \
-	$(LIBDL) \
+	$(DL_LIBS) \
 	$(LIBM) \
 	$(SELINUX_LIBS) \
 	$(LIBAUDIT_LIBS)
@@ -597,7 +597,7 @@ libnm_iface_helper_la_LIBADD = \
 	$(GUDEV_LIBS) \
 	$(LIBNL_LIBS) \
 	$(LIBNDP_LIBS) \
-	$(LIBDL) \
+	$(DL_LIBS) \
 	$(LIBM)
 
 nm_iface_helper_SOURCES = \

src/ppp-manager/Makefile.am

@@ -22,7 +22,7 @@ nm_pppd_plugin_la_LDFLAGS = -module -avoid-version
 
 nm_pppd_plugin_la_LIBADD = \
 	$(GLIB_LIBS) \
-	$(LIBDL) \
+	$(DL_LIBS) \
 	$(NULL)
 
 endif