common.mak: Add '-Wl,--as-needed' to DEFAULT_LDFLAGS

Many distros and buildsystems use '-Wl,--as-needed' default-wise anyway.
For example, Ubuntu, Fedora, and Meson default to '-Wl,--as-needed'.
Considering some of the projects that use/support Meson, e.g. util-linux,
systemd, libvirt, or git, are all built with '-Wl,--as-needed' as well.

So add '-Wl,--as-needed' to DEFAULT_LDFLAGS to also default to that.

Note that with '-Wl,--as-needed' the order of flags, objects, and libraries
matters for the link step. The link rule in common.mak already has the
correct order, so using '-Wl,--as-needed' will not hurt.

    %: %.o
	    $(LINK) $(ALL_LDFLAGS) $^ $(LDLIBS) -o $@

Signed-off-by: Ingo Franzki <ifranzki@linux.ibm.com>
Reviewed-by: Jan Höppner <hoeppner@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

common.mak

@@ -165,7 +165,7 @@ ifeq ("${ENABLE_WERROR}", "1")
 endif
 
 DEFAULT_CPPFLAGS = -D_GNU_SOURCE
-DEFAULT_LDFLAGS = -rdynamic
+DEFAULT_LDFLAGS = -rdynamic -Wl,--as-needed
 
 ifeq ("${ASAN}","1")
 	DEFAULT_CFLAGS  += -fsanitize=address -fno-omit-frame-pointer