init/Kconfig:1036:warning: choice default symbol 'CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE' is not contained in the choice
Cases where the default symbol belongs to the wrong choice are also
detected.
(The mistake is harmless here: Since the default symbol is not visible,
the choice falls back on using the first visible symbol as the default,
which is CC_OPTIMIZE_FOR_PERFORMANCE, as intended.)
Discovered while playing around with Kconfiglib
(https://github.com/ulfalizer/Kconfiglib).