autogen-native: fix POSIX_SHELL and perl

autogen-native: fix POSIX_SHELL and perl

The shebang's length is usually 128 as defined in /usr/include/linux/binfmts.h:
  #define BINPRM_BUF_SIZE 128

So there would be errors when /path/to/hosttools/perl is longer than 128.

This patch fixes the problem when POSIX_SHELL and perl are used as the interpreters.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>