Hmmm, it seems that a C++17-ism has crept into Scintilla LTS version.
My interpretation is that the default implementation of `Scintilla::UniqueStringSet::UniqueStringSet()` is not `noexcept` because although C++11 defined `noexcept` it was not until C++17 that the `std::vector` default constructor was made `noexcept` so the default constructor for `Scintilla::UniqueStringSet::UniqueStringSet` cannot be `noexcept` and so it conflicts with the explicitly specified `noexcept`.
#2506 appears to fix that, just needs to be tested, maybe you could try it.