Upgrade autogen.sh on PostGIS 2.4, 2.5, 3.0

[robe]

It seems many with autoconf > 2.69 are struggling to compile PostGIS 2.4 and 2.5 and possibly 3.0 chains.

So I think we should backport some of the changes we made in 3.1 to those.

We can mark as a breaking change if needed. My desktop autoconf running 2.69 works fine with 3.1 and 3.2 and that has been out for a while.

[robe]

Okay looks like the reason 3.1 and 3.2 work is because of Raul's patches to autogen.sh.

I'm going to test that out and backport.

Most of his changes were to change exit to exit 1 and touch build-aux/config.rpath which is actually where winnie is complaining.

[Regina Obe <lr@…>]

In 1814f8a2/git:

Backport autogen.sh changes from 3.1 to address autoconf 2.71, references #4968 for PostGIS 2.5.6

[Regina Obe <lr@…>]

In f6e37c3/git:

Backport autogen.sh changes from 3.1 to address autoconf 2.71, references #4968 for PostGIS 3.0.4

[Regina Obe <lr@…>]

In 4f4b2005/git:

Backport autogen.sh changes from 3.1 to address autoconf 2.71, closes #4968 for PostGIS 2.4.10. Fix cu_measures test Closes #4963 Closes 4326 for PostGIS 2.4.10