CHECK_CXX_SOURCE_COMPILES ignores compiler flags on macOS

[tkemmer]

On macOS, the configuration script ignores additional compiler flags when performing C++ compilation checks, caused explicitly by: https://github.com/BALL-Project/ball/blob/c66bb528461e9e3a772a3be8223eb0f560fba7b9/cmake/BALLConfiguration.cmake#L104-L107

This behavior results in some C++11 language features being disabled on macOS although being supported. Currently affected feature guards:

• BALL_HAS_THREAD_LOCAL
• BALL_HAS_NOEXCEPT
• BALL_HAS_STD_STRING_CONST_ITERATOR_INITLIST_INSERT

Removing the condition from the code above solves this problem. However, this causes the FindXDR CMake macro to fail, disabling persistence support as a consequence.