libc: make more use of the howmany() macro when available.

We have a howmany() macro in the <sys/param.h> header that is
convenient to re-use as it makes things easier to read.

lib/libc/db/btree/bt_open.c

@@ -277,7 +277,7 @@ __bt_open(const char *fname, int flags, int mode, const BTREEINFO *openinfo, int
 		b.cachesize = b.psize * MINCACHE;
 
 	/* Calculate number of pages to cache. */
-	ncache = (b.cachesize + t->bt_psize - 1) / t->bt_psize;
+	ncache = howmany(b.cachesize, t->bt_psize);
 
 	/*
 	 * The btree data structure requires that at least two keys can fit on

lib/libc/db/hash/hash.c

@@ -160,8 +160,7 @@ __hash_open(const char *file, int flags, int mode,
 		 * maximum bucket number, so the number of buckets is
 		 * max_bucket + 1.
 		 */
-		nsegs = (hashp->MAX_BUCKET + 1 + hashp->SGSIZE - 1) /
-			 hashp->SGSIZE;
+		nsegs = howmany(hashp->MAX_BUCKET + 1, hashp->SGSIZE);
 		if (alloc_segs(hashp, nsegs))
 			/*
 			 * If alloc_segs fails, table will have been destroyed