I just tried updating to Gnome 3.8 and GCC 4.8, and it seems that all of my installed Gnome 3.8 packages compiles fine, except gnome-nettool.

Minor issue with some casts it seems. I've translated the compiler errors from Swedish to English, so the might not be word-by-word correct in regards to its English version.

x86_64-pc-linux-gnu-gcc -DHAVE_CONFIG_H -I. -I.. -DGNOME_NETTOOL_LOCALEDIR=\""/usr/share/locale"\" -DUI_DIR=\""/usr/share/gnome-nettool/ui/"\" -DPIXMAPS_DIR=\""/usr/share/gnome-nettool/pixmaps"\" -pthread -I/usr/include/gtk-3.0 -I/usr/include/at-spi2-atk/2.0 -I/usr/include/gtk-3.0 -I/usr/include/gio-unix-2.0/ -I/usr/include/cairo -I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0 -I/usr/include/atk-1.0 -I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2 -I/usr/include/libdrm -I/usr/include/gdk-pixbuf-2.0 -I/usr/include/libpng16 -I/usr/include/libgtop-2.0 -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include     -march=native -O2 -pipe  -Wall -Wstrict-prototypes -Wnested-externs -Werror=missing-prototypes -Werror=implicit-function-declaration -Werror=pointer-arith -Werror=init-self -Werror=format-security -Werror=format=2 -Werror=missing-include-dirs  -c lookup.c
info.c: I funktion ”info_nic_update_stats”:
info.c:235:2: error: format ”%lld” expecting argument of the type ”long long int”, but argument 3 is of type ”guint64” [-Werror=format=]
  g_sprintf (rx_pkt, "%lld", netload.packets_in);
  ^
info.c:236:2: error: format ”%lld” expecting argument of the type ”long long int”, but argument 3 is of type ”guint64” [-Werror=format=]
  g_sprintf (tx_pkt, "%lld", netload.packets_out);
  ^
info.c:238:2: error: format ”%lld” expecting argument of the type ”long long int”, but argument 3 is of type ”guint64” [-Werror=format=]
  g_sprintf (rx_error, "%lld", netload.errors_in);
  ^
info.c:239:2: error: format ”%lld” expecting argument of the type ”long long int”, but argument 3 is of type ”guint64” [-Werror=format=]
  g_sprintf (tx_error, "%lld", netload.errors_out);
  ^
info.c:241:2: error: format ”%lld” expecting argument of the type ”long long int”, but argument 3 is of type ”guint64” [-Werror=format=]
  g_sprintf (collisions, "%lld", netload.collisions);
  ^
cc1: some warnings treated as error
make[2]: *** [info.o] error 1
make[2]: *** Inväntar oavslutade jobb...
make[2]: Lämnar katalogen "/var/tmp/portage/net-analyzer/gnome-nettool-3.8.0/work/gnome-nettool-3.8.0/src"
make[1]: *** [all-recursive] error 1
make[1]: Lämnar katalogen "/var/tmp/portage/net-analyzer/gnome-nettool-3.8.0/work/gnome-nettool-3.8.0"
make: *** [all] error 2
 * ERROR: net-analyzer/gnome-nettool-3.8.0 failed (compile phase):
 *   emake failed
 * 
 * If you need support, post the output of `emerge --info '=net-analyzer/gnome-nettool-3.8.0'`,
 * the complete build log and the output of `emerge -pqv '=net-analyzer/gnome-nettool-3.8.0'`.
 * The complete build log is located at '/var/tmp/portage/net-analyzer/gnome-nettool-3.8.0/temp/build.log'.
 * The ebuild environment file is located at '/var/tmp/portage/net-analyzer/gnome-nettool-3.8.0/temp/environment'.
 * Working directory: '/var/tmp/portage/net-analyzer/gnome-nettool-3.8.0/work/gnome-nettool-3.8.0'
 * S: '/var/tmp/portage/net-analyzer/gnome-nettool-3.8.0/work/gnome-nettool-3.8.0'


Reproducible: Always

Steps to Reproduce:
1.Unmask GCC 4.8
2.Unmask Gnome 3.8
3.Select GCC 4.8 via gcc-config
4.Update gnome-nettool