top,ps: improve /proc/PID/cmdinfo reading code

function                                             old     new   delta
display_status                                         -    1231   +1231
read_cmdline                                           -     101    +101
parse_conf                                          1284    1303     +19
arith                                               2033    2042      +9
collect_blk                                          467     474      +7
fsck_main                                           1909    1911      +2
dhcprelay_main                                      1125    1122      -3
singlemount                                         4555    4547      -8
read_close                                            50      36     -14
get_lcm                                              123     105     -18
ed_main                                             3111    3084     -27
func_args                                             73      28     -45
procps_scan                                          732     658     -74
top_main                                            2187     899   -1288
------------------------------------------------------------------------------
(add/remove: 2/0 grow/shrink: 4/8 up/down: 1369/-1477)       Total: -108 bytes
   text    data     bss     dec     hex filename
 676048    2744   13968  692760   a9218 busybox_old
 675940    2744   13968  692652   a91ac busybox_unstripped

libbb/read.c

@@ -124,11 +124,11 @@ char *xmalloc_reads(int fd, char *buf)
 
 ssize_t read_close(int fd, void *buf, size_t size)
 {
-	int e;
+	/*int e;*/
 	size = full_read(fd, buf, size);
-	e = errno;
+	/*e = errno;*/
 	close(fd);
-	errno = e;
+	/*errno = e;*/
 	return size;
 }