[clang] [clang-tools-extra] [llvm] [ADT] Refactor StringMap iterators (NFC) (PR #156137)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `bolt-x86_64-ubuntu-nfc` running on `bolt-worker` while building `clang-tools-extra,clang,llvm` at step 13 "nfc-check-bolt".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/92/builds/23180

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

```
Step 13 (nfc-check-bolt) failure: 1200 seconds without output running b'nice -n 5 ninja check-bolt', attempting to kill
...
PASS: BOLT :: X86/dwarf5-debug-line-print.s (546 of 556)
PASS: BOLT :: X86/jump-table-ambiguous-unreachable.s (547 of 556)
PASS: BOLT :: X86/dwarf5-two-cus.s (548 of 556)
PASS: BOLT :: AArch64/missing-code-marker.s (549 of 556)
PASS: BOLT :: binary-analysis/AArch64/trap-instructions.s (550 of 556)
PASS: BOLT :: X86/hlt-terminator.s (551 of 556)
PASS: BOLT :: AArch64/data-marker-invalidates-extra-entrypoint.s (552 of 556)
PASS: BOLT :: dump-dot-func.test (553 of 556)
PASS: BOLT :: AArch64/lite-mode.s (554 of 556)
PASS: BOLT :: AArch64/long-jmp-one-stub.s (555 of 556)
command timed out: 1200 seconds without output running b'nice -n 5 ninja check-bolt', attempting to kill
process killed by signal 9
program finished with exit code -1
elapsedTime=1842.178056

```

</details>

https://github.com/llvm/llvm-project/pull/156137