regression tests for bugs in first versions of new passwd code

[Rich Felker <dalias@libc.org>]

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Here are a couple of tests, in the libc-test framework, for bugs that
affected the early versions of the new passwd code. I'd like to
eventually get some more extensive functionality coverage tests, but
these are a start.

Rich

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// commit fc5a96c9c8aa186effad7520d5df6b616bbfd29d
// getpwnam_r should not crash on nonexistant users when errno is 0

#include <pwd.h>
#include "test.h"

int main(void)
{
	struct passwd *pw, pwbuf;
	char buf[1024];
	getpwnam_r("nonsensical_user", &pwbuf, buf, sizeof buf, &pw);
	return t_status;
}

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// commit 0afef1aa24b784c86ae6121ca39e999824086c7c
// preexisting errno should not be interpreted by passwd/group functions

#include <pwd.h>
#include <errno.h>
#include "test.h"

int main(void)
{
	int baderr = EOWNERDEAD; // arbitrary absurd error
	struct passwd *pw, pwbuf;
	char buf[1024];
	errno = baderr;
	if (getpwnam_r("nonsensical_user", &pwbuf, buf, sizeof buf, &pw) == baderr)
		t_error("getpwnam_r used preexisting errno for nonexisting user\n");
	return t_status;
}