add arm64 Linux support

Author: soxfox42

examples/version.cal

@@ -1,22 +1,30 @@
 include "cores/select.cal"
 include "std/io.cal"
 
-# will execute on RM86 backend
+# Print a different message for each core
+
 version RM86
 	"Hello, RM86!\n" printstr
 end
 
-# will execute on Linux86 backend
-version Linux86
-	"Hello, Linux86!\n" printstr
+version x86_64
+	"Hello, x86_64!\n" printstr
+end
+
+version arm64
+	"Hello, arm64!\n" printstr
+end
+
+version UXN
+	"Hello, Uxn!\n" printstr
 end
 
-# won't execute unless you set the Foo version
+# Specify arbitrary versions to use them as compile-time flags
 version Foo
-	"Hello, Foo!\n" printstr
+	"Foo is enabled :D\n" printstr
 end
 
-# will execute because Foo isn't set
+# This one will run by default unless you set Foo
 version not Foo
-	"Hello, not Foo!\n" printstr
+	"Foo is not enabled :(\n" printstr
 end

source/app.d

@@ -13,6 +13,7 @@ import callisto.preprocessor;
 import callisto.backends.lua;
 import callisto.backends.uxn;
 import callisto.backends.rm86;
+import callisto.backends.arm64;
 import callisto.backends.x86_64;
 
 const static string usage = "
@@ -45,6 +46,7 @@ Flags:
 Backends and their operating systems:
 	rm86   - Real mode x86, for bare-metal, dos
 	x86_64 - 64-bit x86, for bare-metal, linux
+	arm64  - 64-bit ARM, for linux
 	uxn    - Varvara/Uxn
 	lua    - Lua, uses subset CallistoScript
 
@@ -162,6 +164,10 @@ int main(string[] args) {
 							backend = new BackendX86_64();
 							break;
 						}
+						case "arm64": {
+							backend = new BackendARM64();
+							break;
+						}
 						case "uxn": {
 							backend = new BackendUXN();
 							break;