Why AC_C_CHAR_UNSIGNED?

[Hallvard B Furuseth]

What's the point of the AC_C_CHAR_UNSIGNED macro?
    "If the C type `char' is unsigned, define `__CHAR_UNSIGNED__',
    unless the C compiler predefines it."

This is what <limits.h> is for.  If you want to know if char is
unsigned, try #if CHAR_MIN == 0.  I would suggest at least mentioning
that option in the doc for AC_C_CHAR_UNSIGNED.

Though you might warn about things like #if '\300 > 0, because (a) I
think the preprocessor and compiler may have different char types, and
(b) in theory you might someday meet a compiler with 16-bit char.

-- 
Hallvard