tools/autoconf: bump to 2.71

tools/autoconf: bump to 2.71

Autoconf release 2.71 is a bugfix release of 2.70
Links provided are the changelog of 2.70 [1] [2]
and the announcement of 2.71 [3]

The first patch needed to be rewritten.
Some of the lines in the patch were moved
to be consistent with the same change added upstream
in other similar files.

Second and third patches are no longer needed,
Emacs can now be disabled at the configure stage,
and support for musl was added upstream.

The patch now causes help2man to be required
for installing man pages, but we don't need them.
There is no way to disable man pages build
with the configure script,
so use make to touch the files with the build target install-man1.

Link: https://lists.gnu.org/archive/html/autotools-announce/2020-12/msg00001.html
Link: https://lwn.net/Articles/839395
Link: https://lists.gnu.org/archive/html/info-gnu/2021-01/msg00017.html
Signed-off-by: Michael Pratt <mcpratt@pm.me>