Tried to install sys-fs/quota on Gentoo install today and received this error when compiling:
cannot find any C preprocessor (cpp)
The ( quick and easy ) solution seems to be to create a symlink to point /lib/cpp to /lib64/cpp, like this:
ln -s /lib64/cpp /lib/cpp
I’m not sure if using a non-multilib version of Gentoo has caused this, but creating the symlink before compiling ( and removing afterwards ) seems to fix the issue.