Fix build with Qt5

When I build PCL on Ubuntu 13.04 on I get the following error:

```
[  0%] Building CXX object common/CMakeFiles/pcl_common.dir/src/point_types.cpp.o
c++: fatal error: no input files
compilation terminated.
/bin/sh: 1: -fPIE: not found
/bin/sh: 1: -fPIE: not found
/bin/sh: 1: -fPIE: not found
/bin/sh: 1: -fPIE: not found
/bin/sh: 1: -fPIE: not found
make[2]: *** [common/CMakeFiles/pcl_common.dir/src/point_types.cpp.o] Error 127
make[1]: *** [common/CMakeFiles/pcl_common.dir/all] Error 2
make: *** [all] Error 2
```

This patch fixes it.