[llvm] [ADT] Deprecate variadic `StringSwitch::Cases`. NFC. (PR #166066)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-aarch64-sve-vla` running on `linaro-g3-02` while building `llvm` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/17/builds/12330

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

```
Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'HWAddressSanitizer-aarch64 :: TestCases/Linux/fixed-shadow.c' FAILED ********************
Exit Code: 127

Command Output (stdout):
--
# RUN: at line 4
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/./bin/clang    -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta   -gline-tables-only -fsanitize=hwaddress -fuse-ld=lld -mllvm -hwasan-globals -mllvm -hwasan-use-short-granules -mllvm -hwasan-instrument-landing-pads=0 -mllvm -hwasan-instrument-personality-functions /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/compiler-rt/test/hwasan/TestCases/Linux/fixed-shadow.c -o /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/runtimes/runtimes-bins/compiler-rt/test/hwasan/AARCH64/TestCases/Linux/Output/fixed-shadow.c.tmp
# executed command: /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/./bin/clang -Wthread-safety -Wthread-safety-reference -Wthread-safety-beta -gline-tables-only -fsanitize=hwaddress -fuse-ld=lld -mllvm -hwasan-globals -mllvm -hwasan-use-short-granules -mllvm -hwasan-instrument-landing-pads=0 -mllvm -hwasan-instrument-personality-functions /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/llvm/compiler-rt/test/hwasan/TestCases/Linux/fixed-shadow.c -o /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/runtimes/runtimes-bins/compiler-rt/test/hwasan/AARCH64/TestCases/Linux/Output/fixed-shadow.c.tmp
# RUN: at line 5
/home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/runtimes/runtimes-bins/compiler-rt/test/hwasan/AARCH64/TestCases/Linux/Output/fixed-shadow.c.tmp
# executed command: /home/tcwg-buildbot/worker/clang-aarch64-sve-vla/stage1/runtimes/runtimes-bins/compiler-rt/test/hwasan/AARCH64/TestCases/Linux/Output/fixed-shadow.c.tmp
# .---command stdout------------
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...

```

</details>

https://github.com/llvm/llvm-project/pull/166066