MSVC: Enable control flow guard for release builds

This makes the applications and libraries more safe
and won't cause any binary incompatibility.

It's not supported for MSVC 2015, but since we only
support MSVC 2019 or later in Qt6, it's safe to use
this parameter.

The "-guard:cf" parameter is supported by clang-cl
and intel-cl as well, MinGW doesn't support it.

[1] https://docs.microsoft.com/en-us/cpp/build/reference/guard-enable-control-flow-guard?view=msvc-160
[2] https://docs.microsoft.com/en-us/cpp/build/reference/guard-enable-guard-checks?view=msvc-160

Change-Id: I7b035b4b0f22617a7f3c067cddde0bed2e13dd1c
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

cmake/QtInternalTargets.cmake

@@ -167,7 +167,7 @@ if (MSVC)
             -FS
             -Zc:rvalueCast
             -Zc:inline
-    )
+        )
     endif()
     if (MSVC_VERSION GREATER_EQUAL 1899)
         target_compile_options(PlatformCommonInternal INTERFACE
@@ -192,9 +192,13 @@ if (MSVC)
 
     target_compile_options(PlatformCommonInternal INTERFACE -Zc:wchar_t)
 
+    target_compile_options(PlatformCommonInternal INTERFACE
+        $<$<NOT:$<CONFIG:Debug>>:-guard:cf>
+    )
+
     target_link_options(PlatformCommonInternal INTERFACE
         -DYNAMICBASE -NXCOMPAT
-        $<$<NOT:$<CONFIG:Debug>>:-OPT:REF -OPT:ICF>
+        $<$<NOT:$<CONFIG:Debug>>:-OPT:REF -OPT:ICF -GUARD:CF>
     )
 endif()
 

mkspecs/features/qt_module.prf

@@ -336,4 +336,13 @@ win32 {
 }
 DEFINES *= QT_DEPRECATED_WARNINGS_SINCE=0x060000
 
+msvc {
+    QMAKE_CFLAGS_RELEASE                  += -guard:cf
+    QMAKE_CFLAGS_RELEASE_WITH_DEBUGINFO   += -guard:cf
+    QMAKE_CXXFLAGS_RELEASE                += -guard:cf
+    QMAKE_CXXFLAGS_RELEASE_WITH_DEBUGINFO += -guard:cf
+    QMAKE_LFLAGS_RELEASE                  += /GUARD:CF
+    QMAKE_LFLAGS_RELEASE_WITH_DEBUGINFO   += /GUARD:CF
+}
+
 TARGET = $$qt5LibraryTarget($$TARGET$$QT_LIBINFIX)  # Do this towards the end