Add aarch64 execution infrastructure

aarch64-hello.s

@@ -0,0 +1,5 @@
+.global _main
+
+_main:
+    mov x0, 42  // exit code
+    ret

runtime.s

@@ -0,0 +1,5 @@
+.global main
+main:
+    bl _main
+	mov x8, 93 	// sys_exit() is at index 93 in kernel functions table
+	svc #0 		// generate kernel call sys_exit(123);

test-aarch64-run.scm

@@ -0,0 +1,11 @@
+#lang racket
+
+(require "test-util.scm")
+
+(test-eq
+ (compile-arm-asm "aarch64-hello.s" "a.out")
+ #t)
+
+(test-eq
+ (run-arm-executable "a.out")
+ 42)

test-util.scm

@@ -1,7 +1,14 @@
 #lang racket
 
-(provide test-eq)
+(require racket/system)
+
+(provide test-eq compile-arm-asm run-arm-executable)
 
 (define (test-eq a b)
    (if (equal? a b) (displayln "PASS") (error (format "FAIL: ~a != ~a" a  b))))
 
+(define (compile-arm-asm filename outfilename)
+  (system (format "aarch64-linux-gnu-gcc -static ~a runtime.s -o ~a" filename outfilename)))
+
+(define (run-arm-executable filename)
+  (system/exit-code (format "qemu-aarch64 ./~a" filename)))