The config is loaded from json files by qmake, and we define the qmake
function `swiftConfig` for checking whether a feature is enabled.
This function can be directly used in `buildconfig_gen.cpp.in`,
so the trick with C++ comment tokens in variables is not needed.
Depending on the branch, we override the end of live date relative in month
from the build time.
develop/ builds expire in 6 month
release/ builds expire in 12 month
all others expire in 3 month.
ref T319
