[Patch] Fix ac_c99_complex configury

[Benjamin Kosnik]

> If it works, great! Yesterday, I did some experiments outside the
> configury, "by hand" and was under the impression that indeed (as you
> explained in the current comment) the backward/complex.h was picked,
> then everything goes nuts ;)

It works, sorry for not making that clear.

tested x86/linux

> Ah, now I see! The point is, when the C++ compiler is used by
> *configure*, include/backward is *not* in the path!!! Do you say, in the
> US: "Columbus egg?" ;)

Right. Actually, -nostdc++ is in the compile line, and there are no
libstdc++ includes at configure time. So, configure's test looks like this:

%/mnt/hd/bld/gcc/./gcc/xgcc -shared-libgcc -B/mnt/hd/bld/gcc/./gcc/ -nostdinc++ -L/mnt/hd/bld/gcc/i686-pc-linux-gnu/libstdc++-v3/src -L/mnt/hd/bld/gcc/i686-pc-linux-gnu/libstdc++-v3/src/.libs -B/mnt/hd/bld/H-x86-gcc/i686-pc-linux-gnu/bin/ -B/mnt/hd/bld/H-x86-gcc/i686-pc-linux-gnu/lib/ -isystem /mnt/hd/bld/H-x86-gcc/i686-pc-linux-gnu/include -isystem /mnt/hd/bld/H-x86-gcc/i686-pc-linux-gnu/sys-include -H -c complex_conf.cc
. /usr/include/complex.h
.. /usr/include/features.h
... /usr/include/sys/cdefs.h
... /usr/include/gnu/stubs.h
.. /usr/include/bits/mathdef.h
.. /usr/include/bits/cmathcalls.h
.. /usr/include/bits/cmathcalls.h
.. /usr/include/bits/cmathcalls.h


Anyway. There has been a lot of configure movement, perhaps when I
initially did this things were wonky. In any case, this particular hack
is not needed any longer, so let's remove it.

-benjamin