Utils: Join SynchronousProcess::run and runBlocking implementations

Make functionality dependent on an (intentionally ugly)
setProcessUserEventWhileRunning call.

Also, back-paddle a bit on API combination of QtcProcess and
SynchronousPrceoss for now and prevent the QtcProcess-and-
runBlocking and SynchronousProcess-and-start combinations.

Goal is still to have all in QtcProcess in the end, but this
may take a while.

Change-Id: Ic146ec5db0ab8dc9613e5b2af5f4dc90bc7465ca
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/ios/iosprobe.cpp

@@ -68,7 +68,8 @@ void XcodeProbe::detectDeveloperPaths()
     Utils::SynchronousProcess selectedXcode;
     selectedXcode.setTimeoutS(5);
     selectedXcode.setCommand({"/usr/bin/xcode-select", {"--print-path"}});
-    selectedXcode.run();
+    selectedXcode.setProcessUserEventWhileRunning();
+    selectedXcode.runBlocking();
     if (selectedXcode.result() != QtcProcess::Finished)
         qCWarning(probeLog)
                 << QString::fromLatin1("Could not detect selected Xcode using xcode-select");