Splitting configure.ac

[Magnus Ihse Bursie]

The configure.ac file had grown to monsterous proportions, and mostly 
without any clear structure. :-)

I have now chopped the monster apart, and sorted it into 
reasonable-sized bags. (Almost a bit too visual metaphor... :-))

My goal was to have configure.ac basically only containing the overall 
structure of the configuration process, and put the specific logic into 
separate files. The separate files that currently exists are:

* basics.m4 -- basic helper functions and core autoconf/configuration 
support
* boot-jdk.m4 -- stuff related to the BootJDK
* builddeps.m4 -- stuff related to builddeps (still barely even a tech 
preview...)
* build-performance.m4 -- stuff that just are used to affect build 
performance (like ccache etc)
* help.m4 -- user support
* jdk-options.m4 -- stuff related to configure options which are very 
JDK specific, like "--with-jvm-variant".
* libraries.m4 -- stuff related to external (and sometimes also 
internal) libraries
* platform.m4 -- stuff related to openjdk build and target platform.
* source-tree.m4 -- stuff related to the structuring of the forest 
(--with-add-source-root etc)
* toolchain.m4 -- stuff related to the "toolchain", i.e. compilers and 
friends

All of them looks a mess, right now, though. :-& I have not wanted to 
change order of anything, to not risk breaking stuff. As soon as I can I 
will continue clean each of these files up, see how much I can reorder 
and regroup functionality without breaking anything, etc. I'm also 
thinking that one or two of the support files don't have exceptionally 
good names, so there might be some renames coming up.

/Magnus