For those unaware, dev-util/ninja is a make-replacement created by one
of the Chromium guys at Google. Its focus is on making incremental
builds of large software faster.

In the latest chromium ebuild (chromium-29.0.1516.3), we are using ninja
instead of make. ninja auto-detects the number of jobs to run by
default; in the chromium ebuild, we override this by passing -j
$(makeopts_jobs) instead.

Another place ninja is used cmake-utils.eclass, where it may be used
optionally in place of make depending on the CMAKE_MAKEFILE_GENERATOR
variable. The ninja_src_make function in cmake-utils.eclass calls ninja
with ${MAKEOPTS} or not depending on the value of CMAKE_VERBOSE. This is
a bit inconsistent and could cause problems because ninja only accepts a
limited subset of GNU make's command line options.

I'm wondering if we should create a more global function for calling
ninja in a consistent way. Maybe we should introduce a NINJAOPTS
variable for users to set in make.conf. Should we create a new eclass
for this, or just stick it in eutils?

Thoughts?