compiler: use macro Unordered_map instead of std::unordered_map

    
    Per gcc/go/go-system.h, this is what it is supposed to be, to
    support wider platforms.
    
    Reviewed-on: https://go-review.googlesource.com/85975

From-SVN: r256389

gcc/go/gofrontend/MERGE

-dbc0c7e4329aada2ae3554c20cfb8cfa48041213
+0445dc01fd75325ff99f839cfaab29cb9f2a1f97
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/escape.cc

@@ -858,7 +858,7 @@ Gogo::analyze_escape()
 
       // Propagate levels across each dst.  This is the flood phase.
       std::set<Node*> dsts = context->dsts();
-      std::unordered_map<Node*, int> escapes;
+      Unordered_map(Node*, int) escapes;
       for (std::set<Node*>::iterator n = dsts.begin();
            n != dsts.end();
            ++n)