[gentoo-dev] cmake-utils.eclass: rewrite of `_ninjaopts_from_makeopts()`

[rindeal]

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Hello everybody,

I've rewritten `_ninjaopts_from_makeopts()` from cmake-utils.eclass. Please
review the change.

Gentoo bug: https://bugs.gentoo.org/show_bug.cgi?id=559064
Github PR: https://github.com/gentoo/gentoo/pull/1228

Regards

Jan