I'm trying to emerge dev-perl/Bit-Vector (versions 6.3-r1 and 6.4), and there seems to be a problem with its dependencies: when compiling the package, it uses the gcc flag "-Wdeclaration-after-statement", but this flag is not defined for <gcc-3.4 (I think). Since it doesn't detect that it needs a higher version of gcc, it tries to compile it, but reports an error and dies.
So? gcc-3.4 is stable, use it. Dependency won't help anything, having gcc-3.4 installed doesn't mean that you've switched to it.
Ok, gcc 3.4 is stable, but the dependencies of dev-perl/Bit-Vector should say: "Bit-Vector needs gcc 3.4 or higher".