mv varnish.m4 varnish-legacy.m4

This file will now contain legacy macros, that is to say shims to deal
with older platforms and macros for out-of-tree VMODs introduced with
Varnish 4.0.0-tp1.

These macros work well but their interfaces aren't ideal and they leave
too much autotools work to downstream VMOD maintainers. They have also
suffered a lack of maintenance, like this 3yo comment:

    # Uses internal function for now..

New macros will be introduced, but the current macros are left as-is and
VMOD maintainers won't be forced to upgrade their build system.

Makefile.am

@@ -6,7 +6,7 @@ pkgconfigdir = $(libdir)/pkgconfig
 pkgconfig_DATA = varnishapi.pc
 
 m4dir = $(datadir)/aclocal
-m4_DATA = varnish.m4
+m4_DATA = varnish-legacy.m4
 
 CLEANFILES = cscope.in.out cscope.out cscope.po.out
 EXTRA_DIST = \
@@ -15,7 +15,7 @@ EXTRA_DIST = \
 	LICENSE \
 	autogen.sh \
 	varnishapi.pc.in \
-	varnish.m4
+	varnish-legacy.m4
 
 DISTCHECK_CONFIGURE_FLAGS = \
     --enable-developer-warnings \

varnish.m4 → varnish-legacy.m4

-# varnish.m4 - Macros to locate Varnish header files.            -*- Autoconf -*-
+# varnish-legacy.m4 - Macros to locate Varnish header files. -*- Autoconf -*-
 # serial 3 (varnish-4.0)
 
 # Copyright (c) 2013-2015 Varnish Software AS