gyp: use all processors instead of hard-coded 8.
gyp: use all processors instead of hard-coded 8.

Makes no difference for me but might help others because gyp can easily
keep lots of processors busy.

BUG=362075
R=scottmg@chromium.org
Review URL: https://codereview.chromium.org/232783007/

Patch from Daniel Bratell <bratell@opera.com>!

witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp