`unshare --user --pid tcsh` hangs tcsh

[siteshwar]

Running unshare --user --pid tcsh on Linux hangs tcsh at startup. It is caused due to disabled interrupts.

Related code:

tcsh/sh.proc.c

Lines 1829 to 1833 in 985b16f

	while ((pid = fork()) == -1)
	if (setintr == 0)
	(void) sleep(FORKSLEEP);
	else
	stderror(ERR_NOPROC);

I suspect trying to change this behaviour may have unintended side effects. Is there a possibility this may be fixed upstream?