[llvm] [PowerPC][NFC] Pre-commit test case for checking whether `mtvsrbmi` power10 instruction not used (PR #143956)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-x86_64-debian-dylib` running on `gribozavr4` while building `llvm` at step 7 "test-build-unified-tree-check-llvm".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/60/builds/30186

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

```
Step 7 (test-build-unified-tree-check-llvm) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/PowerPC/mtvsrbmi.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/b/1/llvm-x86_64-debian-dylib/build/bin/llc < /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll -ppc-asm-full-reg-names  -mtriple=powerpc-ibm-aix -mcpu=pwr10  -verify-machineinstrs    | /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll --check-prefix=CHECK # RUN: at line 9
+ /b/1/llvm-x86_64-debian-dylib/build/bin/llc -ppc-asm-full-reg-names -mtriple=powerpc-ibm-aix -mcpu=pwr10 -verify-machineinstrs
+ /b/1/llvm-x86_64-debian-dylib/build/bin/FileCheck /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll --check-prefix=CHECK
/b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll:22:10: error: CHECK: expected string not found in input
; CHECK: L..CPI0_0:
         ^
<stdin>:37:5: note: scanning from here
 blr
    ^
<stdin>:63:6: note: possible intended match here
 .tc L..CPI0_0[TC],L..CPI0_0
     ^

Input file: <stdin>
Check file: /b/1/llvm-x86_64-debian-dylib/llvm-project/llvm/test/CodeGen/PowerPC/mtvsrbmi.ll

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

Input was:
<<<<<<
            .
            .
            .
           32:  .csect ..text..[PR],5 
           33: ._Z5v00FFv: 
           34: # %bb.0: # %entry 
           35:  lwz r3, L..C0(r2) # %const.0 
           36:  lxv vs34, 0(r3) 
           37:  blr 
check:22'0         X error: no match found
           38: L.._Z5v00FFv0: 
check:22'0     ~~~~~~~~~~~~~~~
           39:  .vbyte 4, 0x00000000 # Traceback table begin 
check:22'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           40:  .byte 0x00 # Version = 0 
check:22'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~
           41:  .byte 0x09 # Language = CPlusPlus 
check:22'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           42:  .byte 0x20 # -IsGlobaLinkage, -IsOutOfLineEpilogOrPrologue 
check:22'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
            .
            .
            .
           58:  .vbyte 4, 0x00000000 # Vector Parameter type =  
check:22'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
...

```

</details>

https://github.com/llvm/llvm-project/pull/143956