[lldb] Handle EOF from `lldb-vscode`

Sometimes (when running lldb-vscode under strace) I get:

read(0, "", 16)                         = 0
read(0, "", 16)                         = 0
read(0, "", 16)                         = 0
...

With this patch testcases finish properly even with strace:

read(0, "", 16)                         = 0
futex(0x1346508, FUTEX_WAKE_PRIVATE, 2147483647) = 0
stat("", 0x7ffe8f2634c8)                = -1 ENOENT (No such file or directory)
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_KILLED, si_pid=9124, si_uid=1001, si_status=SIGINT, si_utime=1, si_stime=0} ---
close(4)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++

Differential Revision: https://reviews.llvm.org/D64698

llvm-svn: 366187