Use vanilla m4 files with known source. Prepared for possible removal at
build time if the system already has autoconf-archive source present.
Switch to AX_PKG_SWIG macro for versioned or unversioned swig detection.
patch to it to not fail when -Werror is also specified, from the
autoconf-archives.
git-svn-id: file:///svn/unbound/trunk@2904 be551aaa-1e26-0410-a405-d3ace91eadb9