Update .gitignore to ignore qmake/qmake_pch.pch

This file is generated when building qmake on Windows

Change-Id: I554bb2d32cfeff6791d664a5ca7b3d605db38c77
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>

.gitignore

@@ -100,6 +100,7 @@ mkspecs/qconfig.pri
 moc_*.cpp
 qmake/qmake.exe
 qmake/Makefile.bak
+qmake/qmake_pch.pch
 src/corelib/global/qconfig.cpp
 src/corelib/global/qconfig.h
 src/corelib/global/qconfig.h.qmake