crossgcc: Update to clang 4.0

crossgcc: Update to clang 4.0

Drop Edward's cfe patch because it has been implemented by
upstream clang differently. Instead of

 $ clang --print-librt-file-name

the right way to get ahold of the compiler-rt builtin library is

 $ clang -rtlib=compiler-rt --print-libgcc-file-name

Change-Id: I8aac5256da5bfb6f7bebeff0959f16b53867c581
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/20274
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>