This PR fixes a bug in EmitC that can be caused by working with the
string literal `"\x01abc"` in
Lean and causes a C compiler error.
The error is as follows:
```
run.c:29:189: error: hex escape sequence out of range
29 | static const lean_string_object l_badString___closed__0_value = {.m_header = {.m_rc = 0, .m_cs_sz = 0, .m_other = 0, .m_tag = 249}, .m_size = 5, .m_capacity = 5, .m_length = 4, .m_data = "\x01abc"};
| ^~~~~~~
1 error generated.
```
This happens as hex escape sequences can be arbitrarily long while lean
expects them to cut off
after two chars. Thus, the C compiler parses the string as one large hex
escape sequence `01abc` and
subsequently notices this is too large.
Discovered by @datokrat
