[gentoo-user] [query] How to avoid installing a particular package(like gcc) in each update

[dell core2duo]

Hi All,
   Each time i run "emerge -auDNv gnome'  some packages got updated each
time. I want to avoid continue update of big packages like gcc,glibc,
because updating these packages took too much time.
Is there any way i can avoid he same ?

TIA,
flukebox