added arm64-ancient build

Added arm64 build for ancient kernels, needed to support Android phones
whose kernels are too old to support kernels used by the current arm64
build.

Updated Android/git-annex-install to use it. (Also made it use i386-ancient
because that seems like a good idea.)

Sponsored-by: Noam Kremen on Patreon

doc/install/Android/git-annex-install

@@ -13,7 +13,7 @@ set -e
 
 case $(uname -m) in
 	aarch64)
-		arch=arm64
+		arch=arm64-ancient
 		;;
 	arm)
 		arch=armel
@@ -22,10 +22,10 @@ case $(uname -m) in
 		arch=armel
 		;;
 	x86_64)
-		arch=amd64
+		arch=amd64-ancient
 		;;
 	x86_32)
-		arch=i386
+		arch=i386-ancient
 		;;
 	*) 
 		echo "unknown architecture $(uname -m), cannot install" >&2