V3 PATCH: numeric_limits<> support, fix PR/3865

[Neil Booth]

Gabriel Dos Reis wrote:-

> | if (L'\0' - 1 < 0)
> |    wchar_t_is_signed;
> | else
> |    wchar_t_is_unsigned;
> 
> That doesn't work with -fshort-wchar.
> 
> Also, that assumes CPP uses (or emulates) the target's integer system
> to do calculations. Is that the case?  

To follow up on my terse reply, the C/C++ front ends use the exact same
code as CPP; it's in cpplib.  Both obey -fshort-wchar (last time I
checked; there may even be a testcase in the testsuite).

If either of these statements is false, then IMO it's a bug that
slipped past me and I'll fix it.

Neil.