If you are using linux >= 3.11 nvidia-drivers will fail compilation.
I had this problem with sys-kernel/hardened-sources-3.11.2.
The attached patch solves the problem for me.
Created attachment 361730 [details, diff]
Please note that, to reproduce this bug, you should probably fix #482784 first.
This bug is present also in x11-drivers/nvidia-drivers-319.60 and, probably, in other version.
(In reply to Faust from comment #3)
> This bug is present also in x11-drivers/nvidia-drivers-319.60 and, probably,
> in other version.
I can confirm this with sys-kernel/gentoo-sources-3.11.6 and x11-drivers/nvidia-drivers-331.17. I also confirm that the aforementioned patch fixes merge of x11-drivers/nvidia-drivers-331.17.
I also see this with non hardened sources.
*** This bug has been marked as a duplicate of bug 447566 ***
May I ask why this bug was marked as duplicate of a bug marked as won't fix?
I didn't read all comments (they are so many and it looks like the discussion strayed many times from the original topic), but I can't see any concerns about the inclusion of this specific patch. At least I can't see any concerns that wouldn't be raised by any other patch in the portage tree.