CMake: Workaround iOS Xcode issue when configuring app

It appears that CMake's Xcode generator default behavior can't really
handle imported object libraries location, which Qt uses extensively
(all the qt_add_resource calls).

Specifically the project fails to configure with the following error
message:
The OBJECT library type may not be used for IMPORTED libraries under
Xcode with multiple architectures.

An issue was filed upstream at
https://gitlab.kitware.com/cmake/cmake/-/issues/21276

In the mean time, it looks like it's possible to work around the issue
by setting XCODE_EMIT_EFFECTIVE_PLATFORM_NAME global property to OFF.
This needs to be done before the very first project() call, so we do
it in the generated Qt toolchain file.

Note that the workaround only works if the CMake project is configured
with a single architecture given to CMAKE_OSX_ARCHITECTURES.
If multiple arches are given, it will fail with the same error
message.

Fixes: QTBUG-87198
Change-Id: I2556ae28b2fc2d9cfe464a5acf9c4fcbaf01b654
Reviewed-by: Joerg Bornemann <joerg.bornemann@qt.io>

cmake/QtBaseGlobalTargets.cmake

@@ -208,6 +208,10 @@ endif()")
         list(APPEND init_platform
             "set(CMAKE_OSX_ARCHITECTURES \"${_qt_osx_architectures_escaped}\" CACHE STRING \"\")")
         unset(_qt_osx_architectures_escaped)
+
+        list(APPEND init_platform "if(CMAKE_GENERATOR STREQUAL \"Xcode\" AND NOT QT_NO_XCODE_EMIT_EPN)")
+        list(APPEND init_platform "    set_property(GLOBAL PROPERTY XCODE_EMIT_EFFECTIVE_PLATFORM_NAME OFF)")
+        list(APPEND init_platform "endif()")
     endif()
 elseif(ANDROID)
     list(APPEND init_platform "set(ANDROID_NATIVE_API_LEVEL \"${ANDROID_NATIVE_API_LEVEL}\" CACHE STRING \"\")")