build: use LDADD/LIBADD

Rather than manipulate LDFLAGS directly, the correct
way to pass additional linked-to libraries is via
the LDADD and LIBADD variables for executables and
libraries respectively.  Convert all cases of -lfoo
to LDADD/LIBADD.

Change-Id: Id5fb8539b3fa875430f297de37ad0f3e4ecc3726
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/Makefile.am b/Makefile.am
index 9b72b3a..2a24517 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -35,7 +35,8 @@
 libsdbusplus_la_SOURCES = \
 	$(LIBSDBUSPLUS_FILES) \
 	$(LIBSDBUPLUS_FILES_TRANSACTION)
-libsdbusplus_la_LDFLAGS = $(SYSTEMD_LIBS) -version-info 1:0:0 -shared
+libsdbusplus_la_LIBADD = $(SYSTEMD_LIBS)
+libsdbusplus_la_LDFLAGS = -version-info 1:0:0 -shared
 libsdbusplus_la_CXXFLAGS = $(SYSTEMD_CFLAGS)
 
 pkgconfiglibdir = ${libdir}/pkgconfig