Xcode: Incorrect optimization level set when using `add_compile_options( -Oz )`

The GCC_OPTIMIZATION_LEVEL Xcode property is still set to -O3 and -Oz is added to OTHER_CPLUSPLUSFLAGS. This is problematic for cases when I want to override the -Oz to -O3 for a specific target using target_compile_options. This then leaves the GCC_OPTIMIZATION_LEVEL of the target on -O3 and does not remove -Oz from targets OTHER_CPLUSPLUSFLAGS.

The problem is that Xcode, when generating an argument list for clang, first puts the contents of GCC_OPTIMIZATION_LEVEL and then OTHER_CPLUSPLUSFLAGS, thus -Oz overrides the -O3.

The CMake should correctly parse the -Oz flag and put it to GCC_OPTIMIZATION_LEVEL Xcode property - it does the same if I use -Os instead. I haven't tested if -Ofast is parsed correctly.

I'm using CMake 3.21.3 and have observed this issue at least from CMake 3.16 (haven't tested with earlier versions of Xcode).