RFR: 8366777: Build fails unknown pseudo-op with old AS on linux-aarch64 [v5]

[SendaoYan]

> Hi all,
> 
> Build jdk on linux-aarch64 with older assembler version(as 2.30) will report compilation failre, shows as [JDK-8366777](https://bugs.openjdk.org/browse/JDK-8366777).
> 
> This PR add the expression `svfloat64_t a() {}` to makefile which will trigger the compilation during configure stage. After this PR, at configure stage will check the gcc and assember support `-march=armv8-a+sve` or not more comprehensive.
> 
> Testing:
> - [x] On linux-aarch64 gcc12.3.1 as2.37, configure set SVE_CFLAGS as '-march=armv8-a+sve'
> - [x] On linux-aarch64 gcc10.3.0 as2.30, configure set SVE_CFLAGS as empty
> 
> 
> The compilation fails demo as below:
> 
> 
> # cat sve.c 
> #include <arm_sve.h>
> svfloat64_t a() {}
> # gcc -march=armv8-a+sve sve.c 
> /tmp/ccVOzMzb.s: Assembler messages:
> /tmp/ccVOzMzb.s:6: Error: unknown pseudo-op: `.variant_pcs'

SendaoYan has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:

 - Merge branch 'master' of github.com:openjdk/jdk into jbs8366777
 - Add the original comments for -ftrivial-auto-var-init=zero
 - Remove prefix whitespace
 - Add configure option --enable-aarch64-sve to enable or disable sve explicitly
 - 8366777: Build fails unknown pseudo-op with old AS on linux-aarch64

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/27073/files
  - new: https://git.openjdk.org/jdk/pull/27073/files/5b049ec9..1e477b84

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=27073&range=04
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=27073&range=03-04

  Stats: 3553 lines in 230 files changed: 2299 ins; 273 del; 981 mod
  Patch: https://git.openjdk.org/jdk/pull/27073.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27073/head:pull/27073

PR: https://git.openjdk.org/jdk/pull/27073