re PR go/89368 (ICE in go/gofrontend/expressions.cc:4669 after r268923)

	PR go/89368
    compiler: write barrier check nil-check policy tweak
    
    Tweak the recipe for generating writeBarrier loads to insure that the
    dereference expr is marked as not requiring a nil check (not needed
    for gccgo, but needed for gollvm).
    
    Fixes https://gcc.gnu.org/PR89368
    
    Reviewed-on: https://go-review.googlesource.com/c/162904

From-SVN: r268948

gcc/go/gofrontend/MERGE

-0563f2d018cdb2cd685c254bac5ceb38396d0a27
+1a74b8a22b2ff7f430729aa87ecb8cea7b5cdd70
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/wb.cc

@@ -904,7 +904,8 @@ Gogo::check_write_barrier(Block* enclosing, Statement* without,
   ref = Expression::make_unary(OPERATOR_AND, ref, loc);
   ref = Expression::make_cast(unsafe_pointer_type, ref, loc);
   ref = Expression::make_cast(puint32_type, ref, loc);
-  ref = Expression::make_unary(OPERATOR_MULT, ref, loc);
+  ref = Expression::make_dereference(ref,
+                                     Expression::NIL_CHECK_NOT_NEEDED, loc);
   Expression* zero = Expression::make_integer_ul(0, ref->type(), loc);
   Expression* cond = Expression::make_binary(OPERATOR_EQEQ, ref, zero, loc);