As a noinst_PROGRAMS, the libtool generated for cross-compiling will be
used, which will mess up the linking. Create a all-local target instead.
Also ensure that building uses always a native version of the tool by
specifying a GTK_UPDATE_ICON_CACHE automake variable.
Finally "config.h" has been created to work for the target platform and
causes problem when cross-compiling. So we temporarily generate a basic
config.h which contains only the strict minimum.
When cross-compiling, instead of depending on a natively built GTK+ (which means
building Glib, ATK, Pango, gdk-pixbuf, libX11...) for gtk-update-icon-cache,
find the host compiler and gdk-pixbuf, and build another gtk-update-icon-cache
with that.
This uses AX_PROG_CC_FOR_BUILD from autostars to find the host compiler, and
assumes that you'd set PKG_CONFIG_FOR_BUILD to a host pkg-config binary.
https://bugzilla.gnome.org/show_bug.cgi?id=691301
