nom optimized build errors

[flip111]

with stable rustc 1.33.0

error[E0554]: #![feature] may not be used on the stable release channel
 --> src/main.rs:1:1
  |
1 | #![feature(const_fn)]
  | ^^^^^^^^^^^^^^^^^^^^^

error[E0554]: #![feature] may not be used on the stable release channel
 --> src/main.rs:2:1
  |
2 | #![feature(cfg_target_feature, target_feature, stdsimd)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

with version 1.34.0-nightly (c1d2d83ca 2019-03-01)

error[E0019]: constant function contains unimplemented expression type
   --> src/combinators.rs:245:12
    |
245 |     return c == '\t' as u8 || (c > 31 && c != 127);
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error[E0019]: constant function contains unimplemented expression type
   --> src/combinators.rs:251:14
    |
251 |     return !(c <= 32 || c >= 127 || c == '(' as u8 || c == ')' as u8 || c == '<' as u8
    |              ^^^^^^^^^^^^^^^^^^^

[flip111]

same problem with "combine-optimized"

[flip111]

this is for the HTTP test by the way