Build vmods as shared objects only

It does not make any kind of sense to build a vmod as a static
library, so tell libtool to only build a shared one.

lib/libvmod_debug/Makefile.am

@@ -11,7 +11,7 @@ vmod_srcdir = $(top_srcdir)/lib/libvmod_debug
 vmodtool = $(top_srcdir)/lib/libvcl/vmodtool.py
 noinst_LTLIBRARIES = libvmod_debug.la
 
-libvmod_debug_la_LDFLAGS = $(AM_LDFLAGS) -module -export-dynamic -avoid-version -rpath /nowhere
+libvmod_debug_la_LDFLAGS = $(AM_LDFLAGS) -module -export-dynamic -avoid-version -shared -rpath /nowhere
 
 libvmod_debug_la_SOURCES = \
 	vmod_debug.c

lib/libvmod_std/Makefile.am

@@ -14,7 +14,7 @@ vmod_srcdir = $(top_srcdir)/lib/libvmod_std
 vmodtool = $(top_srcdir)/lib/libvcl/vmodtool.py
 vmod_LTLIBRARIES = libvmod_std.la
 
-libvmod_std_la_LDFLAGS = $(AM_LDFLAGS) -module -export-dynamic -avoid-version
+libvmod_std_la_LDFLAGS = $(AM_LDFLAGS) -module -export-dynamic -avoid-version -shared
 
 libvmod_std_la_SOURCES = \
 	vmod_std.c \