GCC 8.0.0 Status Report (2018-01-15), Trunk in Regression and Documentation fixes only mode

[Andrew Roberts]

Boot strap on Darwin x86_64 with llvm now seems broken as of last 8.0.0 
snapshot, it still is working fine with 7.2.0.
I've added bug: 83903

x86_64, armv6, armv7, aarch64 all seem fine on linux. I've been building 
with latest gmp (6.1.2), mpfr (4.0.0) and mpc (1.1.) across all my systems.

I observe isl was updated to 0.18 in the download_prerequisites script. 
Are the other's going to get updated before the 8.0.0 release?