Toplevel cleanup: disable Java when libffi not supported

[Tom Tromey]

>>>>> "Joseph" == Joseph S Myers <joseph@codesourcery.com> writes:

Joseph> This patch, relative to a tree with
Joseph> <http://gcc.gnu.org/ml/gcc-patches/2011-04/msg02123.html> applied,
Joseph> continues the cleanup of toplevel cases relating to disabling Java or
Joseph> Java libraries by arranging for Java to be disabled (via
Joseph> unsupported_languages) on targets not supporting libffi

It does make sense to build libjava without libffi.

It just means that libjava has somewhat degraded functionality -- libffi
is needed for the interpreter, for JNI, and for some kinds of reflection
(Method.invoke).

I am not sure if there are any existing targets where libjava works but
libffi does not.  Looking at libjava/configure.host, maybe `arm*-elf'
(but maybe configure.host is out of data, it is certainly possible).

There is also --without-libffi, though; I didn't look to see what your
patch does with this.

A better gate for libjava might be boehm-gc.  It is required to run any
sort of real program.

Joseph> The ideal would be for information about libffi-supported targets to
Joseph> come from a configure fragment in the libffi/ directory, as per item 4
Joseph> in <http://gcc.gnu.org/ml/gcc/2011-03/msg00486.html>.

This would help libjava's configury as well.

Tom