Qt5 support has just been merged to master (78c5195)
This should not make any difference if you want to compile and link
If you want to have a QGIS version that makes use of Qt5, please not that
* You need to have the dependencies also linked against Qt5. You most
likely will not find that prebuilt and will need to do it yourself.
Segfaults of crssync when compiling indicate that there are dependencies
linked against Qt4.
* In particular, check the following libraries:
* Python bindings are completely untested (Both, PyQt4 and PyQt5)
* The class QgsHttpTransaction is no longer supported.