Turn on Control Flow Guard for MSVC builds

The performance impact should be negligible according to the
documentation on msdn.
Closes #9101.

conf.pri.windows

@@ -61,3 +61,8 @@ DEFINES += BOOST_USE_WINAPI_VERSION=0x0501
 
 # Enable stack trace support
 CONFIG += stacktrace
+
+win32-msvc* {
+    QMAKE_CXXFLAGS += "/guard:cf"
+    QMAKE_LFLAGS += "/guard:cf"
+}