Fix autogen.sh extream slow.
Fix autogen.sh extream slow.

This configure.ac is extreme slow on libtool-2.4.6.

From libtool mailing list.

You can workaround/fix this by:
-m4_define([nginx_version], m4_include(nginx_version))
-NGINX_VERSION=nginx_version
+NGINX_VERSION=m4_include([nginx_version])

See also.
http://lists.gnu.org/archive/html/libtool/2015-09/msg00004.html

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