[llvm] [GISel][AArch64] Allow PatLeafs to be imported in GISel which were previously causing warnings (PR #140935)

[Jay Foad via llvm-commits]

jayfoad wrote:

This is causing new warnings in my build:
```[93/1162] Building CXX object lib/Target/ARM/CMakeFiles/LLVMARMCodeGen.dir/ARMInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/ARM/ARMInstructionSelector.cpp:170:
/home/jayfoad2/llvm-release/lib/Target/ARM/ARMGenGlobalISel.inc:588:12: warning: unused variable 'Reg' [-Wunused-variable]
  588 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[130/1143] Building CXX object lib/Target/BPF/CMakeFiles/LLVMBPFCodeGen.dir/GISel/BPFInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/BPF/GISel/BPFInstructionSelector.cpp:60:
/home/jayfoad2/llvm-release/lib/Target/BPF/BPFGenGlobalISel.inc:144:12: warning: unused variable 'Reg' [-Wunused-variable]
  144 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[211/990] Building CXX object lib/Target/Mips/CMakeFiles/LLVMMipsCodeGen.dir/MipsInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/Mips/MipsInstructionSelector.cpp:77:
/home/jayfoad2/llvm-release/lib/Target/Mips/MipsGenGlobalISel.inc:403:12: warning: unused variable 'Reg' [-Wunused-variable]
  403 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[301/879] Building CXX object lib/Target/PowerPC/CMakeFiles/LLVMPowerPCCodeGen.dir/GISel/PPCInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/PowerPC/GISel/PPCInstructionSelector.cpp:86:
/home/jayfoad2/llvm-release/lib/Target/PowerPC/PPCGenGlobalISel.inc:322:12: warning: unused variable 'Reg' [-Wunused-variable]
  322 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[353/842] Building CXX object lib/Target/SPIRV/CMakeFiles/LLVMSPIRVCodeGen.dir/SPIRVInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/SPIRV/SPIRVInstructionSelector.cpp:347:
/home/jayfoad2/llvm-release/lib/Target/SPIRV/SPIRVGenGlobalISel.inc:101:12: warning: unused variable 'Reg' [-Wunused-variable]
  101 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[479/706] Building CXX object lib/Target/RISCV/CMakeFiles/LLVMRISCVCodeGen.dir/GISel/RISCVInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/RISCV/GISel/RISCVInstructionSelector.cpp:180:
/home/jayfoad2/llvm-release/lib/Target/RISCV/RISCVGenGlobalISel.inc:1090:12: warning: unused variable 'Reg' [-Wunused-variable]
 1090 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[483/629] Building CXX object lib/Target/X86/CMakeFiles/LLVMX86CodeGen.dir/GISel/X86InstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/X86/GISel/X86InstructionSelector.cpp:156:
/home/jayfoad2/llvm-release/lib/Target/X86/X86GenGlobalISel.inc:1027:12: warning: unused variable 'Reg' [-Wunused-variable]
 1027 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
[495/497] Building CXX object lib/Target/AMDGPU/CMakeFiles/LLVMAMDGPUCodeGen.dir/AMDGPUInstructionSelector.cpp.o
In file included from /home/jayfoad2/git/llvm-project/llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp:39:
/home/jayfoad2/llvm-release/lib/Target/AMDGPU/AMDGPUGenGlobalISel.inc:2544:12: warning: unused variable 'Reg' [-Wunused-variable]
 2544 |   Register Reg = MO.getReg();
      |            ^~~
1 warning generated.
```

https://github.com/llvm/llvm-project/pull/140935