re PR go/52358 (math FAILs on Solaris 8 and 9)

	PR go/52358
math: Work around bug in Solaris 9 implementation of ldexp.

The bug is that ldexp(-1, -1075) should return -0, but the
Solaris 9 implementation returns +0.

From-SVN: r186913

libgo/go/math/ldexp.go

@@ -16,7 +16,18 @@ package math
 func libc_ldexp(float64, int) float64
 
 func Ldexp(frac float64, exp int) float64 {
-	return libc_ldexp(frac, exp)
+	r := libc_ldexp(frac, exp)
+
+	// Work around a bug in the implementation of ldexp on Solaris
+	// 9.  If multiplying a negative number by 2 raised to a
+	// negative exponent underflows, we want to return negative
+	// zero, but the Solaris 9 implementation returns positive
+	// zero.  This workaround can be removed when and if we no
+	// longer care about Solaris 9.
+	if r == 0 && frac < 0 && exp < 0 {
+		r = Copysign(0, frac)
+	}
+	return r
 }
 
 func ldexp(frac float64, exp int) float64 {