Qt Creator not working after OSX Sierra update

I had previous version Yosemite, but after update to Sierra (10.12.6) certain headers are not found

error: 'stdlib.h' file not found
#include <stdlib.h>
{{ ^}}

I created Xcode project that uses std libs, and that worked. (i.e. Command line tools are installed) so the headers are there, but Qt toolchain just do not found them anymore. MaintenanceTool, reboot, qmake, restart etc. does not help. 

That applies to exisiting project! If I create a new project, that get compiled (i.e. found stdlib.h)

If I "Follow Symbol Under Cursor" on the #include <stdlib.h> in Qt Creator, it finds the header. Therefore it looks more like qmake issue? Yet removing shadow build wont help.