The legacy linux/config.h file has been removed from Linux kernel on October 10 and will not be included in Linux 2.6.19. I'll attach a patch to put in x11-drivers/nvidia-legacy-drivers/files and a -r1 version of the existing ebuild.
Created attachment 99647 [details, diff] files/linux-autoconf.patch
Created attachment 99648 [details] nvidia-legacy-drivers-1.0.7184-r1.ebuild Use the files/linux-autoconf.patch fix
I fixed this, but using a different driver that came from Daniel Drake (dsd) from the nvidia-drivers ebuild.