Precompiled headers support for different platforms and build environments

Documentation says that "qmake supports the use of precompiled headers (PCH) on some platforms and build environments, including:

• Windows
  • nmake
  • Dsp projects (VC 6.0)
  • Vcproj projects (VC 7.0 & 7.1)
• Mac OS X
  • Makefile
    **Xcode
• Unix
  • GCC 3.4 and above

and later on Project Options: "All platforms that support precompiled headers have the configuration option precompile_header set.", Unfortunately
precompile_header is set only in following mkspecs: wince, win32-g++, win32-msvc2003, win32-msvc2005, win32-msvc2008 and win32-msvc2010

Source: http://qt-project.org/doc/qt-4.8/qmake-precompiledheaders.html