QT/LLVM RTTI settings - Undefined reference to `typeinfo' when compiling Qt Everywhere from source

Hi,

When trying to build qt-everywhere-src I keep getting:

undefined reference to `typeinfo for clang::ASTFrontendAction
undefined reference to `typeinfo for clang::ASTConsumer
undefined reference to `typeinfo for clang::DiagnosticConsumer
undefined reference to `typeinfo for clang::PPCallbacks

I don't have the exact errors; because, this is happening at work (and offline). 

*Update - See my comment below to save some time, sorry about that.

I first noticed it when trying to build qt-creator. I was trying to build creator with vcpkg LLVM and Qt libs. When that didn't work I decided to build the Qt libs from source with vcpkg LLVM, I ran into this again so I decided to build LLVM from source. Even after I built a fully functional LLVM+Clang I still get this.

These seem to be related, but don't have solutions:

1.) https://bugreports.qt.io/browse/QTCREATORBUG-17876

2.) https://bugreports.qt.io/browse/QTBUG-85348

3.) https://github.com/KDAB/codebrowser/issues/46

4.) https://lists.llvm.org/pipermail/cfe-dev/2010-November/011944.html 

I'm not really sure if it's something to do with Qt or LLVM/Clang. The 'typeinfo' bit is suspicious, and makes me thing one of the comments (from #3) about LLVM being built with " -fno-rtti" might be the problem, but I searched the LLVM repo for it and none of the occurenced seemed feasible. 

I'd really appreciate any help/suggestions. 

Thanks,

/ZRP