Adds a simple macro which limits the CPU count which is used in the
various build-related macro. Using this macro at the beginning of the
specfile to limit the CPU count directly, or to set the CPU count based
on the amount of memory in the system and a "job size".
The default action if no options are provided is to limit builds to a
single CPU.
number of CPUs will never be set to less than 1
this now outputs build flag overrides to be used with %make_build etc.
add documentation
Signed-off-by: Michel Alexandre Salim <salimma@fedoraproject.org>