Solaris: use sysconf to get processor count

Solaris responds correctly to the same value as Cygwin, so let's use that.

common/cpu.c

@@ -402,7 +402,7 @@ int x264_cpu_num_processors( void )
 #elif SYS_WINDOWS
     return x264_pthread_num_processors_np();
 
-#elif SYS_CYGWIN
+#elif SYS_CYGWIN || SYS_SunOS
     return sysconf( _SC_NPROCESSORS_ONLN );
 
 #elif SYS_LINUX