getpass: use of termios.h problematic

[Simon Josefsson]

Some people are reporting that the getpass module used by GnuTLS
doesn't build on Mingw32.  The problem is a missing termios.h, and
presumably also missing tcgetattr/tcsetattr functions.

Further, lib/getpass.c look quite unreadable.  Even the code in glibc
look much friendlier.

I propose to adopt the current glibc code, and #if HAVE_TERMIOS_H and
#if TCGETATTR protect it.  If there are no objections, I'll propose a
patch within a few days.

Thanks.