Changing our focus Linux target system

Hi all,

Up until now, we (Google/Android) had been focused on Ubuntu 12.04 x86_64 LTS, using a custom libedit (July 2013) and gcc 4.8.2 as our primary target Linux system.

As of today, I’ve upgraded our focus to Ubuntu 14.04 x86_64, building with the clang 3.5 package from Ubuntu and using the stock system libedit. I happen to focus on using the gold linker, but I do switch between that and the bfd linker.

For debug builds using cmake and ninja, I get the following timing numbers on my newly-built Ubuntu 14.04 x86_64-based box on a 32-core machine with a clean build of lldb:

g++ 4.8.2/ld.bfd (stock) linker: 7.5 minutes

g++ 4.8.2/ linker: 6.0 minutes
clang-3.5/ linker: 4.9 minutes