[llvm] [TableGen] Avoid assignmentInAssert warning (PR #139715)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-armv8-quick` running on `linaro-clang-armv8-quick` while building `llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/154/builds/16032

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM :: TableGen/GlobalISelCombinerEmitter/match-table-imms.td' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/llvm-tblgen -I /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/../../../include -gen-global-isel-combiner      -combiners=MyCombiner /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-imms.td |  /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-imms.td # RUN: at line 1
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/llvm-tblgen -I /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/../../../include -gen-global-isel-combiner -combiners=MyCombiner /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-imms.td
+ /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-imms.td
llvm-tblgen: ../llvm/llvm/utils/TableGen/GlobalISelCombinerEmitter.cpp:2615: virtual void (anonymous namespace)::GICombinerEmitter::emitTestSimplePredicate(raw_ostream &): Assertion `ExpectedID == ID && "combine rules are not ordered!"' failed.
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.	Program arguments: /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/llvm-tblgen -I /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/../../../include -gen-global-isel-combiner -combiners=MyCombiner /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-imms.td
#0 0x0820c908 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/llvm-tblgen+0x35c908)
#1 0x0820a300 llvm::sys::RunSignalHandlers() (/home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/llvm-tblgen+0x35a300)
#2 0x0820d1c0 SignalHandler(int, siginfo_t*, void*) Signals.cpp:0:0
#3 0xf0edd6f0 __default_rt_sa_restorer ./signal/../sysdeps/unix/sysv/linux/arm/sigrestorer.S:80:0
#4 0xf0ecdb06 ./csu/../sysdeps/unix/sysv/linux/arm/libc-do-syscall.S:47:0
#5 0xf0f0d292 __pthread_kill_implementation ./nptl/pthread_kill.c:44:76
#6 0xf0edc840 gsignal ./signal/../sysdeps/posix/raise.c:27:6
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /home/tcwg-buildbot/worker/clang-armv8-quick/stage1/bin/FileCheck /home/tcwg-buildbot/worker/clang-armv8-quick/llvm/llvm/test/TableGen/GlobalISelCombinerEmitter/match-table-imms.td

--

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


```

</details>

https://github.com/llvm/llvm-project/pull/139715