[yourdetect]

I think defining terminology here might help.

An attempt:

Language-UB (L-UB): UB according to the guarantees of the language.

Project-compiler-UB (PC-UB): The project picks compilers and compiler settings to create a stronger set of guarantees, that turns some language-UB into not being UB. Examples include turning off the strict aliasing requirement in the used compilers, or a compiler by default defining some language-UB as being defined behavior.

I do not know if such terms might catch on, though. Do they seem reasonable to you?