MSVC: define _CRT_SECURE_NO_WARNINGS for all internal CMake targets

In commit 013abe320680b3dcd3f6d7e4fb4880e590ba10e6, I add
_CRT_SECURE_NO_WARNINGS definition for all Qt internal module targets,
to suppress MSVC warnings like:
warning C4996: 'strncpy': This function or variable may be unsafe.

However, when compiling some internal tools, such as qmake and qdoc,
such warnings also exist. To suppress this kind of warning entirely,
_CRT_SECURE_NO_WARNINGS definition should be added for all Qt internal
targets when using MSVC compiler.

Pick-to: 6.1
Change-Id: I9c37b20672f9d0f470e3e9ea847e5221f43bfc04
Reviewed-by: Yuhang Zhao <2546789017@qq.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

cmake/QtInternalTargets.cmake

@@ -152,6 +152,7 @@ if(WIN32)
     target_compile_definitions(PlatformCommonInternal INTERFACE "UNICODE;_UNICODE")
     if(MSVC)
         target_compile_definitions(PlatformCommonInternal INTERFACE
+            "_CRT_SECURE_NO_WARNINGS"
             "$<$<STREQUAL:$<TARGET_PROPERTY:TYPE>,SHARED_LIBRARY>:_WINDLL>"
         )
     endif()

cmake/QtModuleHelpers.cmake

@@ -358,10 +358,6 @@ function(qt_internal_add_module target)
             )
     endif()
 
-    if(MSVC)
-        list(APPEND defines_for_extend_target _CRT_SECURE_NO_WARNINGS)
-    endif()
-
     qt_internal_extend_target("${target}"
         ${header_module}
         SOURCES ${arg_SOURCES}