libc: Improve {,l,ll,imax}div(3) manpages

Mainly rename numerator parameter of div(3) and ldiv(3) from num to
numer, and explicitly specify what "numer", "denom", and "rem" mean in
the manpages.

MFC after:	3 days
Obtained from:	https://github.com/apple-oss-distributions/libc (partially)
Sponsored by:	Klara, Inc.

Signed-off-by: Sebastian Huber <sebastian.huber@embedded-brains.de>

Author: obiwac

newlib/libc/stdlib/div.c

@@ -79,13 +79,12 @@ No supporting OS subroutines are required.
 #include <stdlib.h>		/* div_t */
 
 div_t
-div (int num,
-	int denom)
+div(int numer, int denom)
 {
 	div_t r;
 
-	r.quot = num / denom;
-	r.rem = num % denom;
+	r.quot = numer / denom;
+	r.rem = numer % denom;
 
 	return (r);
 }

newlib/libc/stdlib/ldiv.c

@@ -80,13 +80,12 @@ No supporting OS subroutines are required.
 #include <stdlib.h>		/* ldiv_t */
 
 ldiv_t
-ldiv (long num,
-        long denom)
+ldiv(long numer, long denom)
 {
 	ldiv_t r;
 
-	r.quot = num / denom;
-	r.rem = num % denom;
+	r.quot = numer / denom;
+	r.rem = numer % denom;
 
 	return (r);
 }