* common/ dir is no more.
* When using distcc, our logic to detect the secondary architecture
didn't work because cmake ran "distcc" instad of "distcc gcc-x86". Add
the missing part to the command-line invocation.
* If we don't do that, ninja will fail building WebKit because of a too
long command line
* CMake will use a "response file" to forward arguments when the
command line gets over the limit (with a safety margin)
* Avoid using sed to do regex matching when cmake has built-in
equivalents
* Simplify checks for empty variables (they resolve to false)
* Rewrite the history so each commit can be applied individually
without breaking any functionality
