I was following the instructions from https://www.cilkplus.org/build-gcc-cilkplus, and I consistently got an error saying that "tm.h": no file or directory was found. I'm not sure what tm.h is, or what package it is included with.
I installed the following packages: GNAT (probably doesn't help), GMP, MPFR, MPC, ISL, Flex, Bison.
My configuration options were `./configure --prefix=/usr/lib/gcc/cilkplus --enable-languages="c,c++" --disable-multilib`
On Ubuntu 14.10.