Compile flags (-fPIE) for position independent code

Qt5 is built and packaged with the -reduce-relocations configure option as
default. This causes compilations to run with the -Bsymbolic-functions option,
which makes function pointer comparison ineffective, unless the -fPIE flag is
also supplied.

Change-Id: I61d13993e0cc6fee2e38e8a124e32459f6203d40