android: update configure.ac to support building only with NDK>=15

Change-Id: I638019895921082b9da36315c2f6d3ed98e5249a
Reviewed-on: https://gerrit.libreoffice.org/39127Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>

configure.ac

@@ -381,12 +381,16 @@ if test -n "$with_android_ndk"; then
     fi
     case $ANDROID_NDK_VERSION in
     r9*|r10*)
+        AC_MSG_ERROR([Bulding for Android is only supported with NDK versions above 15.0.*])
         ;;
-    11.1.*|12.1.*|13.1.*|14.1.*|15.0*)
+    11.1.*|12.1.*|13.1.*|14.1.*)
+        AC_MSG_ERROR([Bulding for Android is only supported with NDK versions above 15.0.*])
+        ;;
+    15.0.*)
         ;;
     *)
-        AC_MSG_WARN([Untested android NDK version $ANDROID_NDK_VERSION, only versions r9* til 15.0.* have been used successfully. Proceed at your own risk.])
-        add_warning "Untested android NDK version $ANDROID_NDK_VERSION, only versions r9* til 15.0.* have been used successfully. Proceed at your own risk."
+        AC_MSG_WARN([Untested android NDK version $ANDROID_NDK_VERSION, only version 15.0.* have been used successfully. Proceed at your own risk.])
+        add_warning "Untested android NDK version $ANDROID_NDK_VERSION, only version 15.0.* have been used successfully. Proceed at your own risk."
         ;;
     esac