On Solaris the ncurses header may define an `__attribute__` macro.
This breaks C++ headers that use `__attribute__(...)` syntax.
Somehow it causes references to unresolved symbols:
__gthrw_pthread_once
__gthrw_pthread_mutex_lock
__gthrw_pthread_mutex_unlock
instead of references to the correct symbols:
pthread_once
pthread_mutex_lock
pthread_mutex_unlock
Detect this case and undefine the `__attribute__` macro after
including the curses headers.
3b7be02480