libgo: Build math package with -ffp-contract=off on non-x86.

http://golang.org/issue/7074 shows that not using
-ffp-contract=off produces the wrong result for math.Log2(1)
on arm64.

From-SVN: r208505

libgo/configure

@@ -14985,6 +14985,8 @@ $as_echo "$libgo_cv_c_fancymath" >&6; }
 MATH_FLAG=
 if test "$libgo_cv_c_fancymath" = yes; then
   MATH_FLAG="-mfancy-math-387 -funsafe-math-optimizations"
+else
+  MATH_FLAG="-ffp-contract=off"
 fi
 
 

libgo/configure.ac

@@ -620,6 +620,8 @@ CFLAGS=$CFLAGS_hold])
 MATH_FLAG=
 if test "$libgo_cv_c_fancymath" = yes; then
   MATH_FLAG="-mfancy-math-387 -funsafe-math-optimizations"
+else
+  MATH_FLAG="-ffp-contract=off"
 fi
 AC_SUBST(MATH_FLAG)