We should directly check the values of the debug and optimization
options instead.
get_option('buildtype') will return 'custom' for most combinations
of -Doptimization and -Ddebug, but those two will always be set
correctly if only -Dbuildtype is set. So we should look at those
options directly.
For the two-way mapping between buildtype and optimization
-
debug, see this table: https://mesonbuild.com/Builtin-options.html#build-type-options