check_c_source_compiles("
#include <sys/types.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
	char buf;
	int rv, fdout=1;

	if ((rv = write(fdout, (void *)&buf, 1)) < 1) { return (1); }
	if ((rv = read(0, (void *)&buf, 1)) < 1) { return (1); }
	if (unlink(\"/tmp/foo\") != 0) { return (1); }
	return (0);
}
" _MK_HAVE_UNISTD_H)