I know this is a gcc 4.x issue, I also found some pages about fixing this, but unfortunatly not for gentoo ...
Can send the detailed gcc error later, I'm not at the gentoo machine right now.
Maybe there are patches for vnc-4.1*, but that depends on xorg 7.1, which is still masked.
Use 4.1.2, nothing we could do here.
You could set vnc 4.1.2 stable :-)
Read Bug 145371, please.