RFR: 8263649: AArch64: update cas.m4 to match current AD file

[Nick Gasson]

There's a block of code in aarch64.ad that was generated from cas.m4 and
is surrounded by:

  // BEGIN This section of the file is automatically generated. Do not edit --------------

However this section has been modified several times since it was
generated and no longer matches the output of the M4 file. This patch
updates cas.m4 to reflect the current code.

-------------

Commit messages:
 - 8263649: AArch64: update cas.m4 to match current AD file

Changes: https://git.openjdk.java.net/jdk/pull/3045/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3045&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8263649
  Stats: 65 lines in 2 files changed: 19 ins; 10 del; 36 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3045.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3045/head:pull/3045

PR: https://git.openjdk.java.net/jdk/pull/3045