Kawa build changes: removed gcj support but easier Windows builds

Kawa build changes: removed gcj support but easier Windows builds

[Per Bothner]

I checked in some changes to the Kawa configure+make build system.

I ripped out the support for building with GCJ - which hasn't worked
for a while, due to GCJ not supporting newer Java features.

This simplification made feasible a change so that you can now build
*without* a C compiler, as long as you don't configure with 
--enable-kawa-frontend.
This works around an autoconf limitation such that AC_PROG_CC can't be
conditional, in which case a C compiler is required.  The solution was
to move AC_PROG_CC to a new bin/configure.ac, which is ugly.

I also fixed some problems with building on Windows using configure+make.
This now mostly works under MinGW/MSys.  (I tested it under a slow but
functional ASUS Transformer Book T100, btw.)  There is still two problems
with the doc directory (requiring nroff, plus what looks like an old version
of makeinfo), but those can be worked around.  Furthermore, many of the
tests work.  I haven't looked closely at the failures - some seem to
be related UTF-8 vs Windows character encodings.

Hopefully, this will make it easier for those of you who primarily
use Windows.  Patches welcome for any remaining problems.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/