Port to certain Android environments with no GUI

* configure.ac (USER_FULL_NAME): Define to
android_user_full_name only when a GUI system is being built.
Otherwise, set to pw->pw_gecos or NULL consistently with the
presence of pw->pw_gecos.

* src/editfns.c (Fuser_full_name): Adjust to match.  Accept NULL
values from USER_FULL_NAME.

configure.ac

@@ -2464,11 +2464,6 @@ AC_DEFINE_UNQUOTED([SYSTEM_TYPE], ["$SYSTEM_TYPE"],
   [The type of system you are compiling for; sets 'system-type'.])
 AC_SUBST([SYSTEM_TYPE])
 
-# Check for pw_gecos in struct passwd; this is known to be missing on
-# Android.
-
-AC_CHECK_MEMBERS([struct passwd.pw_gecos], [], [], [#include <pwd.h>])
-
 pre_PKG_CONFIG_CFLAGS=$CFLAGS
 pre_PKG_CONFIG_LIBS=$LIBS
 
@@ -2754,6 +2749,17 @@ AC_SUBST([ANDROID_BUILD_CFLAGS])
 AC_SUBST([ANDROID_SHARED_USER_ID])
 AC_SUBST([ANDROID_SHARED_USER_NAME])
 
+# Check for pw_gecos in struct passwd; this is known to be missing on
+# Android.
+
+AH_TEMPLATE([USER_FULL_NAME], [How to get a user's full name.])
+AC_CHECK_MEMBERS([struct passwd.pw_gecos], [], [], [#include <pwd.h>])
+AS_IF([test x"$REALLY_ANDROID" = "xyes"],
+  [AC_DEFINE([USER_FULL_NAME], [android_user_full_name (pw)])],
+  [AS_IF([test x"$ac_cv_member_struct_passwd_pw_gecos" = "xyes"],
+    [AC_DEFINE([USER_FULL_NAME], [pw->pw_gecos])],
+    [AC_DEFINE([USER_FULL_NAME], [NULL])])])
+
 if test "${with_pgtk}" = "yes"; then
   window_system=pgtk
 fi
@@ -6460,9 +6466,6 @@ AC_SUBST([SEPCHAR])
 dnl Everybody supports this, except MS-DOS.
 AC_DEFINE([subprocesses], [1], [Define to enable asynchronous subprocesses.])
 
-AC_DEFINE([USER_FULL_NAME], [pw->pw_gecos], [How to get a user's full name.])
-
-
 AC_DEFINE([DIRECTORY_SEP], ['/'],
   [Character that separates directories in a file name.])
 

src/editfns.c

@@ -1247,11 +1247,10 @@ is in general a comma-separated list.  */)
   if (!pw)
     return Qnil;
 
-#if defined HAVE_ANDROID && !defined ANDROID_STUBIFY
-  p = android_user_full_name (pw);
-#else
   p = USER_FULL_NAME;
-#endif
+  if (!p)
+    return Qnil;
+
   /* Chop off everything after the first comma, since 'pw_gecos' is a
      comma-separated list. */
   q = strchr (p, ',');