iOS: Define QT_NO_PROCESS, as the platform doesn't allow fork/exec

Change-Id: I0928c4aaa0c308ee86b9611beeba3937b61e226c
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@theqtcompany.com>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@theqtcompany.com>

src/corelib/global/qglobal.h

@@ -585,6 +585,10 @@ class QDataStream;
 #  define QT_NO_SOCKS5
 #endif
 
+#if defined(Q_OS_IOS)
+#  define QT_NO_PROCESS
+#endif
+
 inline void qt_noop(void) {}
 
 /* These wrap try/catch so we can switch off exceptions later.