[winrt support] Disabling usage of some banned APIs for the Windows Runtime

Adding a macro for turning on/off for debugger support. Attaching a debugger is disabled if running tests for the Windows Runtime.

Disabled some usage of environment variables, which aren't avaliable, when under the Windows Runtime.

Replaced one usage of CreateFileA, which isn't allow in the Windows Runtime with fopen.
I think it would be better to add definitions like
``
#if !defined(UNDER_CE) && !BOOST_PLAT_WINDOWS_RUNTIME
  #define BOOST_TEST_HAS_GETENV_SUPPORT
  #define BOOST_TEST_HAS_SETENV_SUPPORT  
#endif 
``
and then to propagate these macros in the code, like in `cpp_main.cpp`