Clang Static Analyzer fails on c-files and c++-files with c++17 features

In my cmake project I have the libtiff c-library as a subdirectory. With the recent release of QtCreator 4.6.0 I tried the clang static analyzer and it produces a ton of errors for the c-files of libtiff:

error: invalid argument '-std=c++14' not allowed with 'C'

which result in errorcode 1.

The use of -std=c++14 is seems to be wrong here. However even for the cpp-files it is used, but that is also wrong as I used set(CMAKE_CXX_STANDARD 17) in my cmakelists.txt to set c++17. MSVC does recognize it and compiles the code just fine.

clang on the other hand does also report errors for c++17 features.