Configury changes to build libstdc++ headers

[Stephen M. Webb]

This is a patch to the configury and build for libstdc++ to do a few things.

(1) move the rules to build certain target-specific sources out of the
configuration phase and into the build phase because make is better at
tracking prerequisite changes than autoconf is.

(2) simplify the header file directory structure in the build tree to match that
in the installation tree, which should simplify installation and testing (not to
mention making just a little more sense).

(3) copy all headers into the build tree instead of some in the build tree
and some in the source tree.

(4) all target-specific headers will go in the target-specific install
directory so side-by-side crosses don't clobber each other.

A ChangeLog entry might be:

----- cut -----
    * include/Makefile.am: New file encapsulating header generation rules.
    * Makefile.am: Added reference to the include subdirectory.
    * acinclude.m4: Moved rules for building sources into various Makefiles.
    * configure.in: Added include/Makefile to AC_OUTPUT.
    * testsuite_flags.in: Changed build-includes to match new header scheme.
    * libio/Makefile.am: Changed INCLUDES to match new scheme.
    * libmath/Makefile.am: Same.
    * libsupc++/Makefile.am: Same.
    * src/Makefile.am: Moved rules to build headers out, sources in.
    * mkc++config: Removed.
----- cut -----

No derived files have been included to save (my) bandwidth.

This patch was bootstrapped and tested successfully on an i686-pc-linux-gnu
platform.  Well, as successfully as without this patch.

There should be two attachments to this email.

 -- 

Stephen M. Webb
stephen at bregmasoft dot com