ext/json/parser/prereq.mk: remove type-limit warning if char is unsigned

Ragel generates a code `0 <= (*p)` where `*p` is char.
As char is unsigned by default on arm and RISC-V, it is warned by gcc:

```
compiling parser.c
parser.c: In function ‘JSON_parse_string’:
parser.c:1566:2: warning: comparison is always true due to limited range of data type [-Wtype-limits]
  if ( 0 <= (*p) && (*p) <= 31 )
  ^
parser.c:1596:2: warning: comparison is always true due to limited range of data type [-Wtype-limits]
  if ( 0 <= (*p) && (*p) <= 31 )
  ^
```

This change removes the warning by substituting the condition with
`0 <= (signed char)(*p)`.

0 files changed, 0 insertions, 0 deletions