re PR go/89598 (go frontend fails to build against mpfr 2.4.2)

	PR go/89598
    compiler: use GMP_RNDN rather than MPFR_RNDN
    
    Missed one last time around.  This fixes the build with mpfr 2.4.2.
    
    Fixes https://gcc.gnu.org/PR89598
    
    Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/165420

From-SVN: r269411

gcc/go/gofrontend/MERGE

-3f8ddaa1d773309b6a4b8e4640f8b9675d9764c6
+9b1374ded3d5e352a655d96bfe1bfb6aa1491a98
 
 The first line of this file holds the git revision number of the last
 merge done from the gofrontend repository.

gcc/go/gofrontend/expressions.cc

@@ -17292,7 +17292,7 @@ Numeric_constant::hash(unsigned int seed) const
       mpfr_clear(m);
       break;
     case NC_FLOAT:
-      f = mpfr_get_d_2exp(&e, this->u_.float_val, MPFR_RNDN) * 4294967295.0;
+      f = mpfr_get_d_2exp(&e, this->u_.float_val, GMP_RNDN) * 4294967295.0;
       val = static_cast<unsigned long>(e + static_cast<long>(f));
       break;
     default: