Turned on threading support.

[SVN r12990]

include/boost/config/compiler/sgi_mipspro.hpp

@@ -11,6 +11,13 @@
 
 #include "boost/config/compiler/common_edg.hpp"
 
+//
+// Threading support:
+// Turn this on unconditionally here, it will get turned off again later
+// if no threading API is detected.
+//
+#define BOOST_HAS_THREADS
 //
 // version check:
 // probably nothing to do here?
+