According to my own experiences and https://forums.gentoo.org/viewtopic-p-7949962.html#7949962, nvidia-drivers fails to compile with TRIM_UNUSED_KSYMS set due to access violations. Example: * ACCESS DENIED: fopen_wr: /usr/src/linux-4.7.2-gentoo/nv-frontend.d /var/tmp/portage/x11-drivers/nvidia-drivers-367.27/work/kernel/nvidia/nv-frontend.c:16:0: fatal error: opening dependency file nv-frontend.d: Permission denied ^ compilation terminated. The ebuild should probably check for it.
*** This bug has been marked as a duplicate of bug 591640 ***