Add CMake 3.9.0-rc3 to coreboot toolchain

Newer versions of clang will need newer versions of CMake (at least
3.4.3) to compile. This patch will enable us to switch to clang 4.0.

Change-Id: I6c91163ce0efd4eb2410cdb433de8be23d510ecd
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/20273
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <philippe.mathieu.daude@gmail.com>
Reviewed-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/crossgcc/sum/cmake-3.9.0-rc3.tar.gz.cksum

@@ -0,0 +1 @@
+d568e74e2e4a1cdeae1820cc2cb36fd2d6afc8fe  tarballs/cmake-3.9.0-rc3.tar.gz