As a follow-up to qtbase commit 083c9269ed73e8771e1dbe10812696b45b7389f3, cmake
versions older than 2.8.12 require now the use of
Qt5<Module>_EXECUTABLE_COMPILE_FLAGS and the use of cmake's
POSITION_INDEPENDENT_CODE feature is not wanted anymore, as it adds -fPIE to
the build flags, which may override -fPIC and thus cause a build issue when
including qglobal.h.

Change-Id: I4dd6e2ea64f5d8ca8a87f874322bc1b1f8ff5392
Reviewed-by: Stephen Kelly <steveire@gmail.com>