Corresponding code is in e.g. GccToolChain::predefinedMacros.

Some thoughts:

• If we want to keep the white list, there should be an easy way to update it, preferably by running a script that queries the toolchain. This could be run when a new version of a toolchain is released.
• It might also make sense to externalize this logic/whitelist. This way fixes in that area could be made/provided by patching a text file (instead of waiting for a new release).