[llvm] [MIRLexer][RISCV] Eat a space after the Machine comment (PR #115365)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-cmake-x86_64-avx512-linux` running on `avx512-intel64` while building `llvm` at step 7 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/133/builds/6626

<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/MIR/skip-mir-comment-trailing-whitespace.mir' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 1: /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/llc /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/CodeGen/MIR/skip-mir-comment-trailing-whitespace.mir -mtriple=riscv64 -mattr=+v -run-pass=none -o - | /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/FileCheck /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/CodeGen/MIR/skip-mir-comment-trailing-whitespace.mir
+ /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/llc /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/CodeGen/MIR/skip-mir-comment-trailing-whitespace.mir -mtriple=riscv64 -mattr=+v -run-pass=none -o -
+ /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/FileCheck /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/CodeGen/MIR/skip-mir-comment-trailing-whitespace.mir
/localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/llc: error: unable to get target for 'riscv64', see --version and --triple.FileCheck error: '<stdin>' is empty.
FileCheck command line:  /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/stage1/bin/FileCheck /localdisk2/buildbot/llvm-worker/clang-cmake-x86_64-avx512-linux/llvm/llvm/test/CodeGen/MIR/skip-mir-comment-trailing-whitespace.mir

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/115365