build: Manage libvcc with libtool

It's still a static library, but the build is slightly more uniform.

bin/varnishd/Makefile.am

@@ -175,7 +175,7 @@ varnishd_CFLAGS = \
 varnishd_LDFLAGS = -export-dynamic
 
 varnishd_LDADD = \
-	$(top_builddir)/lib/libvcc/libvcc.a \
+	$(top_builddir)/lib/libvcc/libvcc.la \
 	$(top_builddir)/lib/libvarnish/libvarnish.la \
 	$(top_builddir)/lib/libvgz/libvgz.a \
 	@JEMALLOC_LDADD@ \

lib/libvcc/Makefile.am

@@ -6,9 +6,9 @@ AM_CPPFLAGS = \
 	-I$(top_srcdir)/include \
 	-I$(top_builddir)/include
 
-noinst_LIBRARIES = libvcc.a
+noinst_LTLIBRARIES = libvcc.la
 
-libvcc_a_SOURCES = \
+libvcc_la_SOURCES = \
 	vcc_compile.h \
 	vcc_namespace.h \
 	vcc_token_defs.h \