Allow to switch off the built-in indexer (globally and per project)

my machine's meekly 16 gib of ram are not enough to work on the whole linux kernel with either code model.

i can put *.c and *.h into "ignore files" in the code model settings to kinda disable the code model, but this being a global setting, it isn't particularly user friendly, nor is the approach very intuitive to start with. (i wonder what that option's originally intended use case is; the tooltip doesn't say.)

therefore, i'd like to see a setting to turn off the code model in the project settings.