[CMake] Ninja: files per second

[Peter Kümmel]

I've added a nice feature to ninja which is now upstream:

By setting the environment variable NINJA_STATUS

bash:
         export NINJA_STATUS="[%s/%t %o(%c)/s] "

cmd.exe (with space at the end):

         set NINJA_STATUS=[%s/%t %o(%c)/s]

Ninja prints the overall processed files per second and the
the current rate of files per second (averaged over the last -j files).

For instance compiling cmake I get (-DCMAKE_BUILD_TYPE=Release):
- Linux   gcc 4.6: [397/397 6.6(12)/s]
- Windows gcc 4.7: [438/438 5.9(11)/s]
- Mac     gcc 4.2: [462/462 4.9(3)/s]

See also
https://github.com/martine/ninja/blob/master/doc/manual.asciidoc#environment-variables

Happy benchmarking,
Peter