more -Wall warning fixes from Cristian Ionescu-Idbohrn.
This time it resulted in small code changes:

function                                             old     new   delta
nexpr                                                820     828      +8
tail_main                                           1200    1202      +2
wrapf                                                166     167      +1
parse_mount_options                                  227     209     -18
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/1 up/down: 11/-18)             Total: -7 bytes

diff --git a/libbb/read.c b/libbb/read.c
index 288358d..fb903c1 100644
--- a/libbb/read.c
+++ b/libbb/read.c
@@ -111,7 +111,7 @@
 {
 	if (count) {
 		ssize_t size = full_read(fd, buf, count);
-		if (size != count)
+		if ((size_t)size != count)
 			bb_error_msg_and_die("short read");
 	}
 }
@@ -160,7 +160,7 @@
 
 	goto jump_in;
 	while (sz < maxsz) {
-		if (p - buf == sz) {
+		if ((size_t)(p - buf) == sz) {
  jump_in:
 			buf = xrealloc(buf, sz + 128);
 			p = buf + sz;