Cannot use c++latest in Visual Studio 2019

In my .pro file, I had

QMAKE_CXXFLAGS += /std:c++latest

defined. 

With Qt 5.11, this worked great and I could use the latest compiler features in visual studio.  Now in Qt 5.12,

/std:c++14

is automatically appended to the visual studio project file's compile options.  I could use

CONFIG += c++17

but then I cannot use the latest features.

Secondarily, we have some internal libraries that have .pri files with

CONFIG += c++14

defined indicating that no matter what, the project must compile using c++14 standards.

It would be nice if CONFIG had a c++latest value or if qmake identified the /std:c++latest compiler flag for visual studio and then did not automatically add /std:c++14 would override lower c+ versions

p.s. when I clicked create, what I typed above reformatted
P.P.S. Joerg took the liberty to fix the format. JIRA can behave weird at times.

P.P.P.S.  I was wrong about the c++14 being added, I had missed a library's .pro file that had it configured.  It still would be nice to have a mechanism to recognize a 'latest' c++ version