libcmd/cmp: report read errors (Solaris patch 045-CR7025778)

This change is pulled from here:
https://github.com/oracle/solaris-userland/blob/master/components/ksh93/patches/045-CR7025778.patch

src/lib/libcmd/cmp.c:
- If a read error occurs, issue an error message.

src/lib/libcmd/cmp.c

@@ -164,12 +164,16 @@ cmp(const char* file1, Sfio_t* f1, const char* file2, Sfio_t* f2, int flags, Sfo
 				return ret;
 			if (!(p1 = (unsigned char*)sfreserve(f1, SF_UNBOUND, 0)) || (c1 = sfvalue(f1)) <= 0)
 			{
+				if (sferror(f1))
+					error(ERROR_exit(2), "read error on %s", file1);
 				if ((e2 - p2) > 0 || sfreserve(f2, SF_UNBOUND, 0) && sfvalue(f2) > 0)
 				{
 					ret = 1;
 					if (!(flags & CMP_SILENT))
 						error(ERROR_exit(1), "EOF on %s", file1);
 				}
+				if (sferror(f2))
+					error(ERROR_exit(2), "read error on %s", file2);
 				return ret;
 			}
 			if (count > 0 && c1 > count)
@@ -181,6 +185,8 @@ cmp(const char* file1, Sfio_t* f1, const char* file2, Sfio_t* f2, int flags, Sfo
 		{
 			if (!(p2 = (unsigned char*)sfreserve(f2, SF_UNBOUND, 0)) || (c2 = sfvalue(f2)) <= 0)
 			{
+				if (sferror(f2))
+					error(ERROR_exit(2), "read error on %s", file2);
 				if (!(flags & CMP_SILENT))
 					error(ERROR_exit(1), "EOF on %s", file2);
 				return 1;