Fix ttyname problem on Android.
* configure.ac: Define macro and conditional HAVE_ANDROID_SYSTEM. * m4/gnupg-ttyname.m4: Force use of replacement on Android. * src/ttyname_r.c: Ditto.
Android's bionic lib has no working ttyname_r() nor ttyname(). Using
them anyway will print
FIX ME! implement ttyname_r() bionic/libc/bionic/stubs.c:466
Thus we force the use of our replacement code which simply return
"/dev/tty".