i386: Use generic exp10f

The generic implementation is twice as fast.  Using the exp10f
benchmark:

 * master:
  "exp10f": {
   "workload-spec2017.wrf (adapted)": {
    "duration": 1.02967e+09,
    "iterations": 4.768e+07,
    "reciprocal-throughput": 18.3579,
    "latency": 24.8331,
    "max-throughput": 5.44725e+07,
    "min-throughput": 4.02688e+07
   }
  }

 * patched:
  "exp10f": {
   "workload-spec2017.wrf (adapted)": {
    "duration": 1.01821e+09,
    "iterations": 6.1984e+07,
    "reciprocal-throughput": 13.1975,
    "latency": 19.6563,
    "max-throughput": 7.57719e+07,
    "min-throughput": 5.08743e+07
   }
  }

Checked on i686-linux-gnu.