Hi everyone, 

I've noticed there is a regression in language version detection in 4.8.0 and 4.8.1, while it works fine in 4.7.2: in CMake-based project that use cotire module(https://github.com/sakra/cotire) language version is always CXX98 even if different version was specified in CMakeLists.txt.
After some analysis I found exact reason why it fails. In abstractmsvctoolchain.cpp there is a function 

bool static hasFlagEffectOnMacros(const QString &flag)

that performs compiler flags filtering, throwing out flags useless for language version detection(currently only /I and /W). It works fine without cotire, but with cotire PCH generation we have /FI flag so sample compilation in MsvcToolChain::msvcPredefinedMacros fails with "Unable to find include bla-blah" error. 

Thanks, 
Vlad. 

UPD: attached minimal CMake project that illustrates the problem and error message screenshot.