[libc] [llvm] [libc] Improve memcpy for ARM Cortex-M supporting unaligned accesses. (PR #144872)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `libc-riscv32-qemu-yocto-fullbuild-dbg` running on `rv32gc-qemu-system` while building `libc,utils` at step 4 "annotate".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/196/builds/9451

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

```
Step 4 (annotate) failure: 'python ../llvm-zorg/zorg/buildbot/builders/annotated/libc-linux.py ...' (failure)
...
[ RUN      ] LlvmLibcImaxAbsTest.Negative
[       OK ] LlvmLibcImaxAbsTest.Negative (52 us)
Ran 3 tests.  PASS: 3  FAIL: 0
[3871/4003] Running unit test libc.test.src.unistd.fpathconf_test
sh: line 1: /timer.3586: Permission denied
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcFpathconfTest.SmokeTest
[       OK ] LlvmLibcFpathconfTest.SmokeTest (3 ms)
Ran 1 tests.  PASS: 1  FAIL: 0
[3872/4003] Running unit test libc.test.src.fcntl.openat_test
FAILED: libc/test/src/fcntl/CMakeFiles/libc.test.src.fcntl.openat_test /home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/build/libc/test/src/fcntl/CMakeFiles/libc.test.src.fcntl.openat_test 
cd /home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/build/libc/test/src/fcntl && /home/libcrv32buildbot/cross.sh libc.test.src.fcntl.openat_test.__build__
sh: line 1: /timer.3602: Permission denied
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcUniStd.OpenAndReadTest
/home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/llvm-project/libc/test/src/fcntl/openat_test.cpp:30: FAILURE
      Expected: 0
      Which is: 0
To be equal to: static_cast<int>(libc_errno)
      Which is: 2
[  FAILED  ] LlvmLibcUniStd.OpenAndReadTest
[ RUN      ] LlvmLibcUniStd.FailTest
[       OK ] LlvmLibcUniStd.FailTest (621 us)
Ran 2 tests.  PASS: 1  FAIL: 1
[3873/4003] Running unit test libc.test.src.fcntl.fcntl_test
sh: line 1: /timer.3599: Permission denied
[==========] Running 7 tests from 1 test suite.
[ RUN      ] LlvmLibcFcntlTest.FcntlDupfd
[       OK ] LlvmLibcFcntlTest.FcntlDupfd (2 ms)
[ RUN      ] LlvmLibcFcntlTest.FcntlGetFl
[       OK ] LlvmLibcFcntlTest.FcntlGetFl (465 us)
[ RUN      ] LlvmLibcFcntlTest.FcntlSetFl
[       OK ] LlvmLibcFcntlTest.FcntlSetFl (507 us)
[ RUN      ] LlvmLibcFcntlTest.FcntlGetLkRead
[       OK ] LlvmLibcFcntlTest.FcntlGetLkRead (1 ms)
[ RUN      ] LlvmLibcFcntlTest.FcntlGetLkWrite
[       OK ] LlvmLibcFcntlTest.FcntlGetLkWrite (422 us)
[ RUN      ] LlvmLibcFcntlTest.UseAfterClose
[       OK ] LlvmLibcFcntlTest.UseAfterClose (569 us)
[ RUN      ] LlvmLibcFcntlTest.SetGetOwnerTest
[       OK ] LlvmLibcFcntlTest.SetGetOwnerTest (757 us)
Ran 7 tests.  PASS: 7  FAIL: 0
[3874/4003] Running unit test libc.test.src.poll.poll_test
sh: line 1: /timer.3600: Permission denied
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcPollTest.SmokeTest
[       OK ] LlvmLibcPollTest.SmokeTest (546 us)
[ RUN      ] LlvmLibcPollTest.SmokeFailureTest
[       OK ] LlvmLibcPollTest.SmokeFailureTest (404 us)
Step 8 (libc-unit-tests) failure: libc-unit-tests (failure)
...
[ RUN      ] LlvmLibcImaxAbsTest.Negative
[       OK ] LlvmLibcImaxAbsTest.Negative (52 us)
Ran 3 tests.  PASS: 3  FAIL: 0
[3871/4003] Running unit test libc.test.src.unistd.fpathconf_test
sh: line 1: /timer.3586: Permission denied
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcFpathconfTest.SmokeTest
[       OK ] LlvmLibcFpathconfTest.SmokeTest (3 ms)
Ran 1 tests.  PASS: 1  FAIL: 0
[3872/4003] Running unit test libc.test.src.fcntl.openat_test
FAILED: libc/test/src/fcntl/CMakeFiles/libc.test.src.fcntl.openat_test /home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/build/libc/test/src/fcntl/CMakeFiles/libc.test.src.fcntl.openat_test 
cd /home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/build/libc/test/src/fcntl && /home/libcrv32buildbot/cross.sh libc.test.src.fcntl.openat_test.__build__
sh: line 1: /timer.3602: Permission denied
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcUniStd.OpenAndReadTest
/home/libcrv32buildbot/bbroot/libc-riscv32-qemu-yocto-fullbuild-dbg/llvm-project/libc/test/src/fcntl/openat_test.cpp:30: FAILURE
      Expected: 0
      Which is: 0
To be equal to: static_cast<int>(libc_errno)
      Which is: 2
[  FAILED  ] LlvmLibcUniStd.OpenAndReadTest
[ RUN      ] LlvmLibcUniStd.FailTest
[       OK ] LlvmLibcUniStd.FailTest (621 us)
Ran 2 tests.  PASS: 1  FAIL: 1
[3873/4003] Running unit test libc.test.src.fcntl.fcntl_test
sh: line 1: /timer.3599: Permission denied
[==========] Running 7 tests from 1 test suite.
[ RUN      ] LlvmLibcFcntlTest.FcntlDupfd
[       OK ] LlvmLibcFcntlTest.FcntlDupfd (2 ms)
[ RUN      ] LlvmLibcFcntlTest.FcntlGetFl
[       OK ] LlvmLibcFcntlTest.FcntlGetFl (465 us)
[ RUN      ] LlvmLibcFcntlTest.FcntlSetFl
[       OK ] LlvmLibcFcntlTest.FcntlSetFl (507 us)
[ RUN      ] LlvmLibcFcntlTest.FcntlGetLkRead
[       OK ] LlvmLibcFcntlTest.FcntlGetLkRead (1 ms)
[ RUN      ] LlvmLibcFcntlTest.FcntlGetLkWrite
[       OK ] LlvmLibcFcntlTest.FcntlGetLkWrite (422 us)
[ RUN      ] LlvmLibcFcntlTest.UseAfterClose
[       OK ] LlvmLibcFcntlTest.UseAfterClose (569 us)
[ RUN      ] LlvmLibcFcntlTest.SetGetOwnerTest
[       OK ] LlvmLibcFcntlTest.SetGetOwnerTest (757 us)
Ran 7 tests.  PASS: 7  FAIL: 0
[3874/4003] Running unit test libc.test.src.poll.poll_test
sh: line 1: /timer.3600: Permission denied
[==========] Running 2 tests from 1 test suite.
[ RUN      ] LlvmLibcPollTest.SmokeTest
[       OK ] LlvmLibcPollTest.SmokeTest (546 us)
[ RUN      ] LlvmLibcPollTest.SmokeFailureTest
[       OK ] LlvmLibcPollTest.SmokeFailureTest (404 us)

```

</details>

https://github.com/llvm/llvm-project/pull/144872