sys-libs/libstdc++-v3 does have emake -j1 in src_install. This seems totally unneeded, it installs fine (tested on different computers with different smp-settings, only distcc not tested) and looking into the cvs-log this seems to mostly be from cleaning up things that have stayed from an old, OLD ebuild and changing from using make to emake. Also I could not find any bugs, open or closed, about failures because of this. If it should break you can always reinstate it.
Bumpy?
it comes more from toolchain.eclass where we see transient bugs from time to time across versions when installing in parallel considering the libstdc++ pkg installs so little, and most of it stuff is serialized in its own code, i doubt -j1 or -j would make any practical difference.
