xlib: Undo debug hack to force fallbacks

Remove the debug hack from

commit f337342c88092a251dc00476c4a9880d1cb90822
Author: Bill Spitzak <spitzak@gmail.com>
Date:   Fri Jul 18 18:46:26 2014 -0700

    V6 image: Use convolution filters for sample reconstruction when downscaling

as it forces the fallback image surface for xlib causing severe
performance degradation.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=82002
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Bill Spitzak <spitzak@gmail.com>
Cc: Bryce Harrington <b.harrington@samsung.com>
Remove LTO support

This just never worked too well and caused too many issues. I don't think anyone
will miss this.

As mentioned in the below bug report, proper LTO support also requires using
special versions of ranlib, nm and ar which support the LTO object files.
Otherwise, calling the normal ranlib on an .a library breaks the list of
exported symbols and thus completely breaks the static library.

This (partly) reverts the following commits:

c3645d97ebd24c6f7ad850785d585aebc706a11c configure.ac: Add a --disable-lto configure option
d486ea30f1a58640a1178de74f705a73845b1cda configure: Conditionally include -flto
0870c6fb5b39dcc04fa376123848adde2d06d2ce gcc-4.5 warnings and optimisation flags.

(The last commit is the one which brought us -flto in the first place even
though it doesn't talk about this. It's also the one which is only reverted
partly.)

Fixes: https://bugs.freedesktop.org/show_bug.cgi?id=77060
CC: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Uli Schlachter <psychon@znc.in>
Reviewed-by: Bryce Harrington <b.harrington@samsung.com>