c: improve patch for UCHAR_MAX etc. problem

c: improve patch for UCHAR_MAX etc. problem

* data/skeletons/c.m4 (b4_c99_int_type_define): Reorder to put the
signed types first, since they’re simpler and this keeps similar
code closer.  For signed types, don’t bother checking whether the
type promotes to int since the type must be signed anyway.  For
unsigned types, protect a test like ‘UCHAR_MAX <= INT_MAX’ with
‘!defined __UINT_LEAST8_MAX__’, as otherwise the logic is wrong
for oddball platforms; and once we do that, there should no need
for ‘defined INT_MAX’ so remove that.