[llvm] [RISCV] Rework memcpy test (PR #120364)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu` running on `sie-linux-worker3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/11289

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

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/RISCV/memcpy.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/llc < /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll -mtriple=riscv32    | /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll --check-prefixes=RV32-BOTH,RV32
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll --check-prefixes=RV32-BOTH,RV32
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/bin/llc -mtriple=riscv32
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll:278:14: error: RV32-NEXT: expected string not found in input
; RV32-NEXT: lbu a2, 14(a1)
             ^
<stdin>:122:18: note: scanning from here
# %bb.0: # %entry
                 ^
<stdin>:123:2: note: possible intended match here
 li a2, 15
 ^
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll:371:14: error: RV32-NEXT: expected string not found in input
; RV32-NEXT: lbu a2, 15(a1)
             ^
<stdin>:132:18: note: scanning from here
# %bb.0: # %entry
                 ^
<stdin>:133:2: note: possible intended match here
 li a2, 16
 ^
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll:468:14: error: RV32-NEXT: expected string not found in input
; RV32-NEXT: lbu a2, 30(a1)
             ^
<stdin>:142:18: note: scanning from here
# %bb.0: # %entry
                 ^
<stdin>:143:2: note: possible intended match here
 li a2, 31
 ^
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll:861:14: error: RV32-NEXT: expected string not found in input
; RV32-NEXT: lbu a2, 30(a1)
             ^
<stdin>:271:18: note: scanning from here
# %bb.0: # %entry
                 ^
<stdin>:272:2: note: possible intended match here
 li a2, 31
 ^

Input file: <stdin>
Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/llvm/test/CodeGen/RISCV/memcpy.ll

-dump-input=help explains the following input dump.

...

```

</details>

https://github.com/llvm/llvm-project/pull/120364