CMake 2.8 does not support default visibility on windows.
To allow building tests add the FREERDP_LOCAL define for each
function that is internal to FreeRDP.
When build with testing these functions are exported and available
for use by tests.
This way we use certain compiler flags (like -msse3) only on files
containing optimized code. This avoids problems that occured when
using these flags compiling generic code and running it on platforms
that don't support these optimizations (i.e. NEON optimization on
ARM platforms).
