[numerics.c.ckdint] Add cross-reference to [basic.fundamental] (cplusplus#8541)

Author: eisenwave

source/numerics.tex

@@ -20648,7 +20648,7 @@
 \pnum
 \mandates
 Each of the types \tcode{type1}, \tcode{type2}, and \tcode{type3} is a
-cv-unqualified signed or unsigned integer type.
+cv-unqualified signed or unsigned integer type\iref{basic.fundamental}.
 
 \pnum
 \remarks