The note implies that the types of constant macros defined in <climits>
may differ from that of C, but no nomative rule say so, and there is no
reason to allow such incompatibilities.

The note was added as the resolution of LWG issue cplusplus#416.
http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#416
But the analysis, which based on rules of integer constants, was wrong:
The type of constant macros are defined in C99 (5.2.4.2.1 p1) by rules
of integer promotions. So LONG_MAX always has type long (integer
promotions has no effect for long), even if the actual range of long and
int are equal. That should hold in C++, too.