Create a simple hello world project ( C++ ) with .pro:

LANGUAGE = C++
TEMPLATE = app
CONFIG += console precompile_header

SOURCES += main.cpp

HEADERS += \
    stable.h

PRECOMPILED_HEADER = stable.h

#ifndef STABLE_H
#define STABLE_H
#include <iostream>
#endif // STABLE_H

This will work with gcc but with clang I get:
make: Entering directory `/home/p/git/cpp/exp/clang/helloworld-build-Desktop-Debug'
mkdir: cannot create directory `helloworld/': File exists

In fact, the directory should probably be helloworld.gch ( or .pch ? ) like in the Makefile generated for gcc.