[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 `clang-aarch64-sve2-vla` running on `linaro-g4-01` while building `llvm` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/198/builds/1078

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

```
Step 7 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM :: CodeGen/RISCV/memcpy.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/stage1/bin/llc < /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/llvm/test/CodeGen/RISCV/memcpy.ll -mtriple=riscv32    | /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/llvm/test/CodeGen/RISCV/memcpy.ll --check-prefixes=RV32-BOTH,RV32
+ /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/llvm/test/CodeGen/RISCV/memcpy.ll --check-prefixes=RV32-BOTH,RV32
+ /home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/stage1/bin/llc -mtriple=riscv32
/home/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/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/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/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/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/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/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/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/tcwg-buildbot/worker/clang-aarch64-sve2-vla/llvm/llvm/test/CodeGen/RISCV/memcpy.ll

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

...

```

</details>

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