[6.0] e4f82eed1 Fix build

[Dridi Boukelmoune]

commit e4f82eed1333ad9075927c9023cbac2ac8a51f8a
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Mon Aug 6 06:29:05 2018 +0000

    Fix build

diff --git a/bin/varnishtest/Makefile.am b/bin/varnishtest/Makefile.am
index fdb640df0..b34caa435 100644
--- a/bin/varnishtest/Makefile.am
+++ b/bin/varnishtest/Makefile.am
@@ -87,7 +87,8 @@ teken_state.h:	$(srcdir)/sequences $(srcdir)/gensequences
 
 vtc_h2_hpack.c: vtc_h2_dectbl.h
 vtc_h2_dectbl.h: huffman_gen.py $(top_srcdir)/include/tbl/vhp_huffman.h
-	$(srcdir)/huffman_gen.py $(top_srcdir)/include/tbl/vhp_huffman.h > $@_
+	$(PYTHON) $(srcdir)/huffman_gen.py \
+	    $(top_srcdir)/include/tbl/vhp_huffman.h > $@_
 	mv $@_ $@
 
 CLEANFILES = $(builddir)/teken_state.h