Add function call test

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

tests/call.asm

@@ -0,0 +1,36 @@
+.section data $0x1000 {
+    factorial:
+        cmplt %r0, $2
+        jnz factorial_one
+
+        push %r0
+        sub %r0, $1
+        call factorial
+        pop %r0
+        mul %status, %r0
+        jmp factorial_end
+
+    factorial_one:
+        mov %status, $1
+    factorial_end:
+        ret
+
+    main:
+        mov %r0, $6
+        call factorial
+        cmpeq %status, $720
+        jz fail
+        mov %status, $0
+        jmp end
+    fail:
+        mov %status, $1
+    end:
+        halt
+
+    .export main
+}
+
+.meta {
+    entry: main
+}
+