libbb: introduce and use nonblock_safe_read(). Yay!

Our shells are immune from this nasty O_NONBLOCK now!

function                                             old     new   delta
nonblock_safe_read                                     -      78     +78
file_get                                             276     295     +19
generateMTFValues                                    428     435      +7
read_line_input                                     1776    1772      -4
preadbuffer                                          543     450     -93
------------------------------------------------------------------------------
(add/remove: 1/0 grow/shrink: 2/2 up/down: 104/-97)             Total: 7 bytes
   text    data     bss     dec     hex filename
 615190     715   23924  639829   9c355 busybox_old
 615168     715   23924  639807   9c33f busybox_unstripped

1 files changed, 2 insertions, 2 deletions

diff --git a/libbb/lineedit.c b/libbb/lineedit.c
index 529344f6c..9aab63702 100644
--- a/libbb/lineedit.c
+++ b/libbb/lineedit.c
@@ -1408,9 +1408,9 @@ int read_line_input(const char *prompt, char *command, int maxsize, line_input_t
         parse_and_put_prompt(prompt);
 
         while (1) {
-                fflush(stdout);
+                fflush(NULL);
 
-                if (safe_read(STDIN_FILENO, &c, 1) < 1) {
+                if (nonblock_safe_read(STDIN_FILENO, &c, 1) < 1) {
                         /* if we can't read input then exit */
                         goto prepare_to_die;
                 }