[Metal] Segfaults when trying to compile `dot2add` for Metal

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```hlsl
StructuredBuffer A : register(t0);
StructuredBuffer B : register(t1);
StructuredBuffer Acc : register(t2);

RWStructuredBuffer Out : register(u3);

[numthreads(1,1,1)]
void main() {
Out[0] = dot2add(A[0], B[0], Acc[0]);
Out[1] = dot2add(A[1], B[1], Acc[1]);
Out[2] = dot2add(A[2], B[2], Acc[2]);
Out[3] = dot2add(A[3], B[3], Acc[3]);
Out[4] = dot2add(A[4], B[4], Acc[4]);
Out[5] = dot2add(A[5], B[5], Acc[5]);
Out[6] = dot2add(A[6], B[6], Acc[6]);
Out[7] = dot2add(A[7], B[7], Acc[7]);
Out[8] = dot2add(A[8], B[8], Acc[8]);
Out[9] = dot2add(A[9], B[9], Acc[9]);
Out[10] = dot2add(A[10], B[10], Acc[10]);
Out[11] = dot2add(A[11], B[11], Acc[11]);

Out[12] = dot2add(half2(1, 2), half2(3, 4), float(0));
Out[13] = dot2add(half2(-1, 2), half2(3, -4), float(10));
Out[14] = dot2add(half2(65504, 1), half2(1, 65504), float(0));
Out[15] = dot2add(half2(1, -65504), half2(-65504, 1), float(-10000000));
}
```

Error messages:
```
Exit Code: 1

Command Output (stdout):
--
Signed DxilContainer written to "/var/folders/zv/v734td6n3_3fl4qmc2hcdkcc0000gn/T/lit-tmp-mn6c6t6w/source-7c69bd.dxo"
Validation succeeded.
--
Command Output (stderr):
--
/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin/split-file /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/OffloadTest/test/Feature/HLSLLib/dot2add.test /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/clang-mtl/Feature/HLSLLib/Output/dot2add.test.tmp # RUN: at line 104
+ /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin/split-file /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/OffloadTest/test/Feature/HLSLLib/dot2add.test /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/clang-mtl/Feature/HLSLLib/Output/dot2add.test.tmp
/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin/clang-dxc -metal --dxv-path=/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/DXC/build/bin -HV 202x -enable-16bit-types -T cs_6_5 -Fo /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/clang-mtl/Feature/HLSLLib/Output/dot2add.test.tmp.o /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/clang-mtl/Feature/HLSLLib/Output/dot2add.test.tmp/source.hlsl # RUN: at line 105
+ /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin/clang-dxc -metal --dxv-path=/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/DXC/build/bin -HV 202x -enable-16bit-types -T cs_6_5 -Fo /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/clang-mtl/Feature/HLSLLib/Output/dot2add.test.tmp.o /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/clang-mtl/Feature/HLSLLib/Output/dot2add.test.tmp/source.hlsl
clang-dxc: error: unable to execute command: Segmentation fault: 11
clang-dxc: error: metal-shaderconverter command failed due to signal (use -v to see invocation)
clang version 22.0.0git (https://github.com/llvm/llvm-project 5165a6c197a0af5b27f6c7f6ac172d09c18623f5)
Target: dxilv1.5-unknown-shadermodel6.5-compute
Thread model: posix
InstalledDir: /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin
Build config: +assertions
clang-dxc: note: diagnostic msg: Error generating preprocessed source(s).
```
```
Exit Code: 139

Command Output (stderr):
--
/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin/split-file /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/OffloadTest/test/Feature/HLSLLib/dot2add.test /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp # RUN: at line 105
+ /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/bin/split-file /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/OffloadTest/test/Feature/HLSLLib/dot2add.test /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp
"/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/DXC/build/bin/dxc-3.7" -metal -enable-16bit-types -T cs_6_5 -Fo /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp.o /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp/source.hlsl # RUN: at line 106
+ /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/DXC/build/bin/dxc-3.7 -metal -enable-16bit-types -T cs_6_5 -Fo /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp.o /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp/source.hlsl
/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.script: line 3: 40539 Segmentation fault: 11 "/Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/DXC/build/bin/dxc-3.7" -metal -enable-16bit-types -T cs_6_5 -Fo /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp.o /Users/cbieneman/actions-runner/_work/offload-test-suite/offload-test-suite/llvm-project/build/tools/OffloadTest/test/mtl/Feature/HLSLLib/Output/dot2add.test.tmp/source.hlsl
```

Start with OffloadTest/test/Feature/HLSLLib/dot2add.test and reproduce the failure using the clang-dxc and dxc-3.7 Metal commands shown in the report. Trace the Metal compilation path around this test to identify the segfault; done means the test completes without either compiler crashing.

Written by the indexing model from the issue text.