SLEEF: fix ldexp
SLEEF: fix ldexp

with certain arguments, ldexp() would return -inf instead of 0:

ldexp3: inf ulp error at {0x1.655946p-71, -2147483648}: *0x0p+0 vs. inf

pocl/pocl,pocl/pocl,Oblomov/pocl,pocl/pocl,pocl/pocl,franz/pocl,franz/pocl,Oblomov/pocl,pocl/pocl,Oblomov/pocl,Oblomov/pocl,franz/pocl,Oblomov/pocl,franz/pocl,franz/pocl