ICU libs shipped with Qt have wrong RPATH on Linux

I've installed Qt 5.11 and 5.12 via the standard maintenance tool of Qt.

The ICU libs shipped with Qt have a wrong, hard-coded, absolute RPATH set up. This should be changed in RUNPATH [$ORIGIN].

The following libs have this issue:

gcc_64/lib/libicudata.so.56.1
gcc_64/lib/libicui18n.so.56.1
gcc_64/lib/libicuio.so.56.1
gcc_64/lib/libicule.so.56.1
gcc_64/lib/libiculx.so.56.1
gcc_64/lib/libicutest.so.56.1
gcc_64/lib/libicutu.so.56.1
gcc_64/lib/libicuuc.so.56.1

To see the problem, run for instance

```
$ readelf -d gcc_64/lib/libicuuc.so.56.1 | grep path
0x000000000000000f (RPATH) Library rpath: [/home/qt/icu_install/lib]
```

as can be seen, the path is hard-coded to be `/home/qt/icu_install/lib`.

I've fixed this manually by setting

```
$ chrpath -c gcc_64/lib/libicuuc.so.56.1
$ chrpath -r "\$ORIGIN" gcc_64/lib/libicuuc.so.56.1
```

which changes RPATH -> RUNPATH and the value to $ORIGIN.

For some 3rd party deployment tools, it is really useful that these incorrect RPATHs are removed.