* lib/gcd.h: Fix typo in last commit.
/* Before including this file, you may define:
GCD_WORD_T The parameter type and result type of the gcd function.
It should be an unsigned integer type that is either
- a built-in type or defined in <stdef.h> or <stdint.h>.
+ a built-in type or defined in <stddef.h> or <stdint.h>.
The definition of GCD_WORD_T needs to be the same across the entire
application. Therefore it is best placed in <config.h>.