QHash freezes due to call to getrandom() via glibc 's getentropy()

sddm is making a blocking call to getrandom(), via the glibc function
getentropy(), via the QRandomGenerator class. Here's a backtrace:

#0  0x00007ffff5ef303a in getentropy (buffer=0x7fffffffe9dc, 
    length=<optimized out>) at ../sysdeps/unix/sysv/linux/getentropy.c:45
#1  0x00007ffff68a2beb in ?? ()
   from target:/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#2  0x00007ffff68a3538 in QHashData::detach_helper(void (*)(QHashData::Node*, void*), void (*)(QHashData::Node*), int, int) ()
   from target:/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#3  0x00007ffff69af7c1 in ?? ()
   from target:/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#4  0x00007ffff69aef3b in QLoggingCategory::defaultCategory() ()
   from target:/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#5  0x00007ffff683d815 in qt_message_output(QtMsgType, QMessageLogContext const&, QString const&) () from target:/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#6  0x00007ffff693bf70 in QDebug::~QDebug() ()
   from target:/usr/lib/x86_64-linux-gnu/libQt5Core.so.5
#7  0x000055555559c870 in SDDM::DaemonApp::DaemonApp(int&, char**) ()
#8  0x000055555557d1c6 in main ()

Reassigning this to Qt as it is not safe to use these functions in a
general-purpose library for Linux.  They should only be used if it's
acceptable to wait some time for entropy to be available.