link failing despite the right linking arguments are presents on command line

Binary package hint: gcc-4.5

Following our conversation on #ubuntu-devel, here is the error on a simple project:
$ gcc -o gnome-settings-daemon/gnome-update-wallpaper-cache `pkg-config --cflags --libs glib-2.0 gdk-2.0 gconf-2.0 gnome-desktop-2.0` debian/gnome-update-wallpaper-cache.c

/tmp/ccpqFpTa.o: In function `main':
gnome-update-wallpaper-cache.c:(.text+0x27): undefined reference to `gdk_init'
gnome-update-wallpaper-cache.c:(.text+0x33): undefined reference to `g_option_context_new'
gnome-update-wallpaper-cache.c:(.text+0x53): undefined reference to `g_option_context_add_main_entries'
gnome-update-wallpaper-cache.c:(.text+0x75): undefined reference to `g_option_context_parse'
gnome-update-wallpaper-cache.c:(.text+0x90): undefined reference to `g_printerr'
gnome-update-wallpaper-cache.c:(.text+0x9c): undefined reference to `g_option_context_free'
gnome-update-wallpaper-cache.c:(.text+0xa8): undefined reference to `g_error_free'
gnome-update-wallpaper-cache.c:(.text+0xc5): undefined reference to `g_option_context_free'
gnome-update-wallpaper-cache.c:(.text+0xca): undefined reference to `gdk_screen_get_default'
gnome-update-wallpaper-cache.c:(.text+0xea): undefined reference to `gdk_screen_get_monitor_geometry'
gnome-update-wallpaper-cache.c:(.text+0xef): undefined reference to `gnome_bg_new'
gnome-update-wallpaper-cache.c:(.text+0xf8): undefined reference to `gconf_client_get_default'
gnome-update-wallpaper-cache.c:(.text+0x110): undefined reference to `gnome_bg_load_from_preferences'
gnome-update-wallpaper-cache.c:(.text+0x13c): undefined reference to `gdk_pixbuf_new'
gnome-update-wallpaper-cache.c:(.text+0x164): undefined reference to `gnome_bg_draw'
collect2: ld returned 1 exit status

-> pkg-config expand normally:
$ pkg-config --cflags --libs glib-2.0 gdk-2.0 gconf-2.0 gnome-desktop-2.0
-pthread -DORBIT2=1 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include -I/usr/include/gtk-2.0 -I/usr/lib/gtk-2.0/include -I/usr/include/gio-unix-2.0/ -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libpng12 -I/usr/include/gconf/2 -I/usr/include/orbit-2.0 -I/usr/include/gnome-desktop-2.0 -I/usr/include/startup-notification-1.0 -I/usr/include/atk-1.0 -pthread -lgconf-2 -lgnome-desktop-2 -lgtk-x11-2.0 -lstartup-notification-1 -lgdk-x11-2.0 -latk-1.0 -lgio-2.0 -lpangoft2-1.0 -lpangocairo-1.0 -lgdk_pixbuf-2.0 -lm -lcairo -lpng12 -lpango-1.0 -lfreetype -lfontconfig -lgobject-2.0 -lgmodule-2.0 -lgthread-2.0 -lrt -lglib-2.0

gcc-4.4 is building it fine.
you can find additional info for a gcc 4.4 build and options there: http://paste.ubuntu.com/532941/
with 4.5: http://paste.ubuntu.com/532940/

I'll attach gnome-update-wallpaper-cache.c to this bug report as well.