In proxychains, we create pipes and use them internally.
If exec() is called by the program we run, the pipes opened
previously are never closed, causing a file descriptor leak
may eventually crash the program.
This commit calls fcntl() to set FD_CLOEXEC flags on pipes.
AFAIK there's no race condition on pipe creation, but we still
prefer to call the newer pipe2() with O_CLOEXEC if it's supported
by the system, due to its advantage of atomic operation, which
prevents potential race conditions in the future.
Signed-off-by: Tom Li <tomli@tomli.me>
11988579f5