ash,hush: fix SIGCHLD interrupting read builtin

function                                             old     new   delta
readcmd                                              169     217     +48
shell_builtin_read                                  1087    1097     +10
localcmd                                             366     364      -2
builtin_read                                         197     193      -4
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/2 up/down: 58/-6)              Total: 52 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-read/read_SIGCHLD.right b/shell/ash_test/ash-read/read_SIGCHLD.right
new file mode 100644
index 0000000..b3dc7ab
--- /dev/null
+++ b/shell/ash_test/ash-read/read_SIGCHLD.right
@@ -0,0 +1,2 @@
+x='Ok'
+exitcode:0