clang-cl supports different MSVC compatibility settings that can be set via -fms-compatibility. clang seems to also support autodetection based on the version of a found cl.exe (see https://reviews.llvm.org/D20136).

However, Qt Creator hardcodes the MSVC initialization script to some (the latest?) MSVC version:

It would be great if we could change the compatibilty, either globally or even per project.

We manually set compatibility in our *.pro file like that:

contains(QMAKE_CXX,clang-cl) {
{{  win32 { }}
{{    QMAKE_CXXFLAGS+=-fms-compatibility}}
{{    QMAKE_CXXFLAGS+=-fms-compatibility-version=18.00.31101}}
{{  { }}
{{{ }}

That work, but it will still include the system headers from MSVC2017, which can result in very strange behaviour/compile time errors.