* If NIX_DEBUG is turned on (set to "1"), autoconf configure scripts
  may fail to find the correct preprocessor:

    checking how to run the C preprocessor... /lib/cpp


* When building gcc using a Nix gcc, generated libraries link against
  the libraries of the latter:

    $ ldd /nix/store/3b1d3995c4edbf026be5c73f66f69245-gcc-3.3.3/lib/libstdc++.so
    ...
    libgcc_s.so.1 => /nix/store/1f19e61d1b7051f1131f78b41b2a0e7e-gcc-3.3.2/lib/libgcc_s.so.1 (0x400de000)
    (wrong! should be .../3b1d.../lib/libgcc_s...)
    ...


* Subtle problems can occur if the Nix store directory or one of its
  parents is a symlink.  E.g., purity checks can barf:

    impure path `/data/nix/store/099cd9aee7d056a9922fd6dd116a3f5c-gcc-3.3.3/bin/../lib/gcc-lib/i686-pc-linux-gnu/3.3.3/crtbegin.o' used in link

  (This happened because /nix was a symlink to /data/nix.)  Maybe we
  should disallow this entirely, since, exactly because it is
  perfectly legal for a builder to expand a symlink, we can end up
  with derivates referring to paths that existed in the build
  environment but not in the target environment.

  Disallowing this can be highly inconvenient, since it makes it
  harder to move the Nix store to a different file system.  (On Linux,
  `bind' mounts can help here.) 


* In libXt:

/bin/sh ./libtool --mode=compile gcc -DHAVE_CONFIG_H -I. -I. -I.     -DXTHREADS -DXUSE_MTSAFE_API -I/nix/store/aadf0bd4a908da11d14f6538503b8408-libX11-6.2.1/include -I/nix/store/ba366e3b944ead64ec9b0490bb615874-xproto-6.6.1/include   -I./include/X11 -g -O2 -c -o ActionHook.lo `test -f 'ActionHook.c' || echo './'`ActionHook.c
mkdir .libs
 gcc -DHAVE_CONFIG_H -I. -I. -I. -DXTHREADS -DXUSE_MTSAFE_API -I/nix/store/aadf0bd4a908da11d14f6538503b8408-libX11-6.2.1/include -I/nix/store/ba366e3b944ead64ec9b0490bb615874-xproto-6.6.1/include -I./include/X11 -g -O2 -c ActionHook.c  -fPIC -DPIC -o .libs/ActionHook.o
In file included from IntrinsicI.h:55,
                 from ActionHook.c:69:
include/X11/IntrinsicP.h:54:27: X11/Intrinsic.h: No such file or directory


* Then:

 gcc -DHAVE_CONFIG_H -I. -I. -I. -DXTHREADS -DXUSE_MTSAFE_API -I/nix/store/aadf0bd4a908da11d14f6538503b8408-libX11-6.2.1/include -I/nix/store/ba366e3b944ead64ec9b0490bb615874-xproto-6.6.1/include -I./include -I./include/X11 -g -O2 -c ActionHook.c  -fPIC -DPIC -o .libs/ActionHook.o
In file included from IntrinsicI.h:55,
                 from ActionHook.c:69:
include/X11/IntrinsicP.h:202:25: X11/ObjectP.h: No such file or directory

(moved to include/X11; should edit include/Makefile.am)


* Doesn't parse:

{stdenv, fetchurl /* pkgconfig, libX11 */ }:

stdenv.mkDerivation {
  name = "libXi-6.0.1";
  src = fetchurl {
    url = http://freedesktop.org/~xlibs/release/libXi-6.0.1.tar.bz2;
    md5 = "7e935a42428d63a387b3c048be0f2756";
  };
/*  buildInputs = [pkgconfig];
  propagatedBuildInputs = [libX11]; */
}