Don't worry - in case things go wrong, the error will be caught before the glibc on your system is replaced. Just make sure you have the latest GCC installed:
emerge -uav sys-devel/gcc
And then make sure it is actually used:
On my system the output looks like this (the star shows the currently used version):
 i686-pc-linux-gnu-4.4.3 *
And here's an example how to change the active GCC version (using the number from above list):
# gcc-config 1
* Switching native-compiler to i686-pc-linux-gnu-4.4.3 ...
For more info, see Gentoo GCC Upgrade Guide.