[llvm] [ADT] Simplify countr_zero and countl_zero with constexpr if (NFC) (PR #141517)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-riscv-rva20-2stage` running on `rise-clang-riscv-rva20-2stage` while building `llvm` at step 4 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/87/builds/1632

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

```
Step 4 (annotate) failure: '../llvm-zorg/zorg/buildbot/builders/annotated/rise-riscv-build.sh --jobs=32' (failure)
...
PASS: lit :: shtest-format.py (81553 of 84683)
PASS: lit :: unparsed-requirements.py (81554 of 84683)
PASS: lit :: test-output-micro-resultdb.py (81555 of 84683)
PASS: lit :: shtest-pushd-popd.py (81556 of 84683)
PASS: lit :: shtest-cat.py (81557 of 84683)
PASS: lit :: unittest-adaptor.py (81558 of 84683)
PASS: lit :: test-output-micro.py (81559 of 84683)
PASS: lit :: test-output.py (81560 of 84683)
PASS: lld :: COFF/alias-implib.s (81561 of 84683)
PASS: lit :: show-result-codes.py (81562 of 84683)
FAIL: lit :: timeout-hang.py (81563 of 84683)
******************** TEST 'lit :: timeout-hang.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 13
not env -u FILECHECK_OPTS "/usr/bin/python3" /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/timeout-hang/run-nonexistent.txt  --timeout=1 --param external=0 | "/usr/bin/python3" /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/stage2/utils/lit/tests/timeout-hang.py 1
# executed command: not env -u FILECHECK_OPTS /usr/bin/python3 /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/timeout-hang/run-nonexistent.txt --timeout=1 --param external=0
# .---command stderr------------
# | lit.py: /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/llvm/llvm/utils/lit/lit/main.py:73: note: The test suite configuration requested an individual test timeout of 0 seconds but a timeout of 1 seconds was requested on the command line. Forcing timeout to be 1 seconds.
# `-----------------------------
# executed command: /usr/bin/python3 /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/stage2/utils/lit/tests/timeout-hang.py 1
# .---command stdout------------
# | Testing took as long or longer than timeout
# `-----------------------------
# error: command failed with exit status: 1

--

********************
PASS: LLVM-Unit :: Support/./SupportTests/10/48 (81564 of 84683)
PASS: lld :: COFF/arm-thumb-branch20-error.s (81565 of 84683)
PASS: lld :: COFF/ar-comdat.test (81566 of 84683)
PASS: lld :: COFF/allow-unknown-debug-info.test (81567 of 84683)
PASS: lld :: COFF/alternatename.test (81568 of 84683)
PASS: lit :: shtest-inject.py (81569 of 84683)
PASS: lld :: COFF/arm64-delayimport.yaml (81570 of 84683)
PASS: lld :: COFF/align.s (81571 of 84683)
PASS: lld :: COFF/arm-thumb-thunks.s (81572 of 84683)
PASS: lld :: COFF/arm64-import2.test (81573 of 84683)
PASS: lld :: COFF/arm-thumb-thunks-multipass.s (81574 of 84683)
PASS: lld :: COFF/arm-thumb-thunks-pdb.s (81575 of 84683)
PASS: lld :: COFF/arm64-localimport-align.s (81576 of 84683)
PASS: lld :: COFF/arm64-magic.yaml (81577 of 84683)
PASS: lld :: COFF/arm64-dynamicbase.s (81578 of 84683)
PASS: lit :: usage.py (81579 of 84683)
PASS: lit :: xunit-output-report-failures-only.py (81580 of 84683)
PASS: lld :: COFF/arm64-relocs-imports.test (81581 of 84683)
Step 11 (llvm-project check-all) failure: llvm-project check-all (failure)
...
PASS: lit :: shtest-format.py (81553 of 84683)
PASS: lit :: unparsed-requirements.py (81554 of 84683)
PASS: lit :: test-output-micro-resultdb.py (81555 of 84683)
PASS: lit :: shtest-pushd-popd.py (81556 of 84683)
PASS: lit :: shtest-cat.py (81557 of 84683)
PASS: lit :: unittest-adaptor.py (81558 of 84683)
PASS: lit :: test-output-micro.py (81559 of 84683)
PASS: lit :: test-output.py (81560 of 84683)
PASS: lld :: COFF/alias-implib.s (81561 of 84683)
PASS: lit :: show-result-codes.py (81562 of 84683)
FAIL: lit :: timeout-hang.py (81563 of 84683)
******************** TEST 'lit :: timeout-hang.py' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 13
not env -u FILECHECK_OPTS "/usr/bin/python3" /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/timeout-hang/run-nonexistent.txt  --timeout=1 --param external=0 | "/usr/bin/python3" /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/stage2/utils/lit/tests/timeout-hang.py 1
# executed command: not env -u FILECHECK_OPTS /usr/bin/python3 /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/llvm/llvm/utils/lit/lit.py -j1 --order=lexical Inputs/timeout-hang/run-nonexistent.txt --timeout=1 --param external=0
# .---command stderr------------
# | lit.py: /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/llvm/llvm/utils/lit/lit/main.py:73: note: The test suite configuration requested an individual test timeout of 0 seconds but a timeout of 1 seconds was requested on the command line. Forcing timeout to be 1 seconds.
# `-----------------------------
# executed command: /usr/bin/python3 /home/buildbot-worker/bbroot/clang-riscv-rva20-2stage/stage2/utils/lit/tests/timeout-hang.py 1
# .---command stdout------------
# | Testing took as long or longer than timeout
# `-----------------------------
# error: command failed with exit status: 1

--

********************
PASS: LLVM-Unit :: Support/./SupportTests/10/48 (81564 of 84683)
PASS: lld :: COFF/arm-thumb-branch20-error.s (81565 of 84683)
PASS: lld :: COFF/ar-comdat.test (81566 of 84683)
PASS: lld :: COFF/allow-unknown-debug-info.test (81567 of 84683)
PASS: lld :: COFF/alternatename.test (81568 of 84683)
PASS: lit :: shtest-inject.py (81569 of 84683)
PASS: lld :: COFF/arm64-delayimport.yaml (81570 of 84683)
PASS: lld :: COFF/align.s (81571 of 84683)
PASS: lld :: COFF/arm-thumb-thunks.s (81572 of 84683)
PASS: lld :: COFF/arm64-import2.test (81573 of 84683)
PASS: lld :: COFF/arm-thumb-thunks-multipass.s (81574 of 84683)
PASS: lld :: COFF/arm-thumb-thunks-pdb.s (81575 of 84683)
PASS: lld :: COFF/arm64-localimport-align.s (81576 of 84683)
PASS: lld :: COFF/arm64-magic.yaml (81577 of 84683)
PASS: lld :: COFF/arm64-dynamicbase.s (81578 of 84683)
PASS: lit :: usage.py (81579 of 84683)
PASS: lit :: xunit-output-report-failures-only.py (81580 of 84683)
PASS: lld :: COFF/arm64-relocs-imports.test (81581 of 84683)

```

</details>

https://github.com/llvm/llvm-project/pull/141517