* 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".
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