[Development] Configure command lines of official Qt releases

[Richard Weickelt]

>> Thanks, Ivan. While this is true for other libs like xcb, Qt does not ship
>> icu. It uses either the one provided by the system or a thin replacement
>> resulting in a reduced localization feature set according to
>> https://wiki.qt.io/Qt_5_ICU#Design_Principles
> 
> Linux binaries are shipped with ICU. It's not possible to use system version, because
> ICU doesn't provide stable ABI.

Good point. Indeed, libQtCore.so links to
	libicui18n.so.56 => /opt/Qt/5.12.3/gcc_64/lib/./libicui18n.so.56
(0x00007f457026f000)
	libicuuc.so.56 => /opt/Qt/5.12.3/gcc_64/lib/./libicuuc.so.56
(0x00007f456feb7000)
	libicudata.so.56 => /opt/Qt/5.12.3/gcc_64/lib/./libicudata.so.56
(0x00007f456e4d4000)

Now I can see how "-R ." makes sense.

By "Qt does not sip icu" I meant that the Qt source package does not ship
icu, but would use whatever it finds on the build host.