[llvm] [MCP] Use MCRegUnit as the key type of CopyTracker::Copies map. NFC. (PR #98277)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lld-x86_64-ubuntu-fast` running on `as-builder-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/432

Here is the relevant piece of the build log for the reference:
```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llc -mtriple=riscv32 -mattr=+m,+d,+zfh,+v,+zvfh      -verify-machineinstrs < /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll | /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll      -check-prefixes=CHECK,CHECK-RV32
+ /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll -check-prefixes=CHECK,CHECK-RV32
+ /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llc -mtriple=riscv32 -mattr=+m,+d,+zfh,+v,+zvfh -verify-machineinstrs
RUN: at line 5: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llc -mtriple=riscv64 -mattr=+m,+d,+zfh,+v,+zvfh      -verify-machineinstrs < /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll | /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll      -check-prefixes=CHECK,CHECK-RV64,CHECK-OPT
+ /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/FileCheck /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll -check-prefixes=CHECK,CHECK-RV64,CHECK-OPT
+ /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/bin/llc -mtriple=riscv64 -mattr=+m,+d,+zfh,+v,+zvfh -verify-machineinstrs
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll:640:19: error: CHECK-OPT-NEXT: is not on the line after the previous match
; CHECK-OPT-NEXT: vsetivli zero, 4, e8, mf4, ta, ma
                  ^
<stdin>:688:2: note: 'next' match was here
 vsetivli zero, 4, e8, mf4, ta, ma
 ^
<stdin>:686:9: note: previous match ended here
# %bb.0:
        ^
<stdin>:687:1: note: non-matching line after previous match is here
 lbu a0, 0(a0)
^
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll:658:19: error: CHECK-OPT-NEXT: is not on the line after the previous match
; CHECK-OPT-NEXT: vsetivli zero, 4, e16, mf2, ta, ma
                  ^
<stdin>:703:2: note: 'next' match was here
 vsetivli zero, 4, e16, mf2, ta, ma
 ^
<stdin>:701:9: note: previous match ended here
# %bb.0:
        ^
<stdin>:702:1: note: non-matching line after previous match is here
 flh fa5, 0(a0)
^

Input file: <stdin>
Check file: /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/test/CodeGen/RISCV/rvv/fixed-vectors-strided-vpload.ll

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

Input was:
<<<<<<
          .
          .
          .
        683:  .variant_cc zero_strided_unmasked_vpload_4i8_i8 
        684: zero_strided_unmasked_vpload_4i8_i8: # @zero_strided_unmasked_vpload_4i8_i8 
        685:  .cfi_startproc 
        686: # %bb.0: 
...

```

https://github.com/llvm/llvm-project/pull/98277