[6.0] 51629df24 Hunt for py-specific variants of sphinx-build program

[Dridi Boukelmoune]

commit 51629df2488fa9c77f8a7bd7b91e3bd05d893af8
Author: Poul-Henning Kamp <phk at FreeBSD.org>
Date:   Thu Oct 11 14:08:51 2018 +0000

    Hunt for py-specific variants of sphinx-build program

diff --git a/configure.ac b/configure.ac
index 13b54b5fb..7db6f51ea 100644
--- a/configure.ac
+++ b/configure.ac
@@ -49,7 +49,9 @@ fi
 AC_ARG_WITH([sphinx-build],
   AS_HELP_STRING([--with-sphinx-build=PATH], [Location of sphinx-build (auto)]),
   [SPHINX="$withval"],
-  AC_CHECK_PROGS(SPHINX, [sphinx-build], [no]))
+  AC_CHECK_PROGS(SPHINX,
+    [sphinx-build sphinx-build-3.6 sphinx-build-2.7],
+    [no]))
 if test "x$SPHINX" = "xno"; then
   AC_MSG_ERROR(
     [sphinx-build is needed to build Varnish, please install python-sphinx.])