The generated-configure.sh script is dead, long live autoconf!

[Magnus Ihse Bursie]

With JDK-8195689 that has just been pushed to jdk/jdk, the checked-in 
runnable generated-configure.sh script has been removed. Instead, 
there's a new build-time dependency on autoconf.

For most users, this should not make any difference. You will still 
initiate your configuration by running "bash configure".

If you do not already have autoconf installed, when running configure 
the first time after checking out JDK-8195689, this will be detected, 
and you will be asked to install autoconf. For most systems, a 
suggestions on how to do this is also printed.

If you have made changes to the build system before, you have probably 
had a work flow including a custom-built autoconf, running autogen.sh, 
and asking someone in Oracle to sponsor your patch for generation of the 
closed version of generated-configure.sh. Neither of this will now be 
needed. While you can of course keep a custom-built version of autoconf, 
you might also delete it. With the new solution, the exact version of 
autoconf does not matter. (Note that it will still be needed for 
backports, though.)

The build documentation has been updated to reflect this change.

/Magnus