[clang] [llvm] [clang][AArch64] Add getHostCPUFeatures to query for enabled features in cpu info (PR #97749)

[LLVM Continuous Integration via cfe-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-x86_64-debian-fast` running on `gribozavr4` while building `clang,llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/56/builds/10880

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'Clang :: Driver/aarch64-mcpu-native.c' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 2: export LLVM_CPUINFO=/b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Driver/Inputs/cpunative/neoverse-v2
+ export LLVM_CPUINFO=/b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Driver/Inputs/cpunative/neoverse-v2
+ LLVM_CPUINFO=/b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Driver/Inputs/cpunative/neoverse-v2
RUN: at line 3: /b/1/clang-x86_64-debian-fast/llvm.obj/bin/clang --target=aarch64 --print-enabled-extensions -mcpu=native | /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck --strict-whitespace --check-prefix=CHECK-FEAT-NV2 --implicit-check-not=FEAT_ /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Driver/aarch64-mcpu-native.c
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/clang --target=aarch64 --print-enabled-extensions -mcpu=native
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck --strict-whitespace --check-prefix=CHECK-FEAT-NV2 --implicit-check-not=FEAT_ /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Driver/aarch64-mcpu-native.c
clang version 20.0.0git (https://github.com/llvm/llvm-project.git d732c0b13c55259177f2936516b6087d634078e0)
Target: aarch64
Thread model: posix
InstalledDir: /b/1/clang-x86_64-debian-fast/llvm.obj/bin
Build config: +assertions
clang: error: unsupported argument 'native' to option '-mcpu='
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck --strict-whitespace --check-prefix=CHECK-FEAT-NV2 --implicit-check-not=FEAT_ /b/1/clang-x86_64-debian-fast/llvm.src/clang/test/Driver/aarch64-mcpu-native.c

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/97749