Build breaks if private headers are installed system wide.

When building Qt master GIT (4.8), building stops because of a wrong file inclusion.

The output looks like this:
compiling[sse] painting/qdrawhelper_sse.cpp
compiling[sse2] image/qimage_sse2.cpp
compiling[sse2] painting/qdrawhelper_sse2.cpp
In file included from image/qimage_sse2.cpp:43:
/usr/include/qt4/QtGui/private/qimage_p.h:106: error: 'QImageWriter' has not been declared
make[1]: *** [.obj/debug-shared/qimage_sse2.o] Error 1
make[1]: *** Waiting for unfinished jobs....
painting/qdrawhelper_mmx.cpp:80: error: 'comp_func_Destination' was not declared in this scope
painting/qdrawhelper_mmx.cpp:88: error: 'comp_func_Plus' was not declared in this scope
painting/qdrawhelper_mmx.cpp:89: error: 'comp_func_Multiply' was not declared in this scope
painting/qdrawhelper_mmx.cpp:90: error: 'comp_func_Screen' was not declared in this scope
painting/qdrawhelper_mmx.cpp:91: error: 'comp_func_Overlay' was not declared in this scope
painting/qdrawhelper_mmx.cpp:92: error: 'comp_func_Darken' was not declared in this scope

So instead of picking the local private header, is including the one installed system-wide.
Should be fixed changing the include directive.