bug#13479: Cross Compiling for ARM

[Ross Biro <ross.biro@mindspring.com>]

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I just more or less successfully compiled emacs-24.2 for a Samsung
Chromebook.  I did it by using the chrooted build environment for
chromiumos.  In the process I learned a couple of things.

I used the configuration:

../emacs-24.2/configure  --build=x86_64-pc-linux-gnu
--host=arm-none-linux-gnueabi --target=arm-none-linux-gnueabi
--with-x-toolkit=no --with-xpm=no --with-jpeg=no --with-png=no
--with-gif=no --with-tiff=no  --without-xml2 --without-gnutls --without-x
--without-dbus --with-crt-dir=/build/arm-generic/usr/lib/

Obviously, I also had to CANNOT_DUMP=yes as well.

1) It doesn't look like emacs has a concept of a BUILDCC.  I like to set CC
to the cross compiler since that seems to be what most things need.
However make-docfile and test-distrib need to be built with the local
compiler.  Usually the path to the local compiler is stored in BUILDCC.  I
just changed the $(CC) to $(BUILDCC) in the makefile for those two file and
everything compiled ok.

2) The lisp and leim directories really want a local copy of emacs to
compile.  Since I didn't have one available in the chrooted environment, I
just used /bin/true.  Suboptimal, but it let the compile complete.  I
didn't see an obvious way to set the path to an external emacs, I just
edited the makefile.

3) Now, a real bug.  With an undumpped emacs,
window__resize_root_window_vertically is called before it's defined.  Even
putting if (initialzed) before the call didn't help.  I had to put  if (!EQ
(XSYMBOL (Qwindow_resize_root_window_vertically)->function, Qunbound))
before the two calls to  call2 (Qwindow_resize_root_window_vertically,  in
window.c.

Now, I'm going to try to and some more libraries and do some additional
testing.  If anyone has questions, email me directly.

    Ross

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