i#1569 AArch64: Disable sign_extend_immed on AArch64.

The automatic sign extension is probably only useful on Intel but
is left enabled on ARM (AArch32) so as not to change the output
from tests (api.disA32, api.disT32, api.static).

This only affects disassembly.

Review-URL: https://codereview.appspot.com/301090043

core/arch/disassemble_shared.c

@@ -985,6 +985,14 @@ sign_extend_immed(instr_t *instr, int srcnum, opnd_t *src)
 {
     opnd_size_t opsz = OPSZ_NA;
     bool resize = true;
+
+#if !defined(X86) && !defined(ARM)
+    /* Automatic sign extension is probably only useful on Intel but
+     * is left enabled on ARM (AArch32) as it is what some tests expect.
+     */
+    return;
+#endif
+
     if (opnd_is_immed_int(*src)) {
         /* PR 327775: force operand to sign-extend if all other operands
          * are of a larger and identical-to-each-other size (since we