[libc] [llvm] [libc][NFC] refactor Cortex `memcpy` code (PR #148204)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `premerge-monolithic-linux` running on `premerge-linux-1` while building `libc,utils` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/153/builds/38297

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

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
...
PASS: lit :: shtest-external-shell-kill.py (98609 of 101601)
PASS: lld :: COFF/duplicate-dwarf.s (98610 of 101601)
PASS: lld :: COFF/defparser.test (98611 of 101601)
PASS: lld :: COFF/dllexport-mingw.s (98612 of 101601)
PASS: lld :: COFF/entry-inference32.test (98613 of 101601)
PASS: lld :: COFF/duplicate.test (98614 of 101601)
PASS: lld :: COFF/entry-drectve.test (98615 of 101601)
PASS: cfi-devirt-lld-thinlto-x86_64 :: cross-dso/icall/dlopen.cpp (98616 of 101601)
PASS: lld :: COFF/entry-weak-external.s (98617 of 101601)
TIMEOUT: MLIR :: Examples/standalone/test.toy (98618 of 101601)
******************** TEST 'MLIR :: Examples/standalone/test.toy' FAILED ********************
Exit Code: 1
Timeout: Reached timeout of 60 seconds

Command Output (stdout):
--
# RUN: at line 1
"/etc/cmake/bin/cmake" "/build/buildbot/premerge-monolithic-linux/llvm-project/mlir/examples/standalone" -G "Ninja"  -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_C_COMPILER=/usr/bin/clang  -DLLVM_ENABLE_LIBCXX=OFF -DMLIR_DIR=/build/buildbot/premerge-monolithic-linux/build/lib/cmake/mlir  -DLLVM_USE_LINKER=lld  -DPython3_EXECUTABLE="/usr/bin/python3.10"
# executed command: /etc/cmake/bin/cmake /build/buildbot/premerge-monolithic-linux/llvm-project/mlir/examples/standalone -G Ninja -DCMAKE_CXX_COMPILER=/usr/bin/clang++ -DCMAKE_C_COMPILER=/usr/bin/clang -DLLVM_ENABLE_LIBCXX=OFF -DMLIR_DIR=/build/buildbot/premerge-monolithic-linux/build/lib/cmake/mlir -DLLVM_USE_LINKER=lld -DPython3_EXECUTABLE=/usr/bin/python3.10
# .---command stdout------------
# | -- The CXX compiler identification is Clang 16.0.6
# | -- The C compiler identification is Clang 16.0.6
# | -- Detecting CXX compiler ABI info
# | -- Detecting CXX compiler ABI info - done
# | -- Check for working CXX compiler: /usr/bin/clang++ - skipped
# | -- Detecting CXX compile features
# | -- Detecting CXX compile features - done
# | -- Detecting C compiler ABI info
# | -- Detecting C compiler ABI info - done
# | -- Check for working C compiler: /usr/bin/clang - skipped
# | -- Detecting C compile features
# | -- Detecting C compile features - done
# | -- Looking for histedit.h
# | -- Looking for histedit.h - found
# | -- Found LibEdit: /usr/include (found version "2.11") 
# | -- Found ZLIB: /usr/lib/x86_64-linux-gnu/libz.so (found version "1.2.11") 
# | -- Found LibXml2: /usr/lib/x86_64-linux-gnu/libxml2.so (found version "2.9.13") 
# | -- Using MLIRConfig.cmake in: /build/buildbot/premerge-monolithic-linux/build/lib/cmake/mlir
# | -- Using LLVMConfig.cmake in: /build/buildbot/premerge-monolithic-linux/build/lib/cmake/llvm
# | -- Linker detection: unknown
# | -- Performing Test LLVM_LIBSTDCXX_MIN
# | -- Performing Test LLVM_LIBSTDCXX_MIN - Success
# | -- Performing Test LLVM_LIBSTDCXX_SOFT_ERROR
# | -- Performing Test LLVM_LIBSTDCXX_SOFT_ERROR - Success
# | -- Performing Test CXX_SUPPORTS_CUSTOM_LINKER
# | -- Performing Test CXX_SUPPORTS_CUSTOM_LINKER - Success
# | -- Performing Test C_SUPPORTS_FPIC
# | -- Performing Test C_SUPPORTS_FPIC - Success
# | -- Performing Test CXX_SUPPORTS_FPIC

```

</details>

https://github.com/llvm/llvm-project/pull/148204