[SPIRV] "Cannot load a runtime-sized array" when initializing local resource via comma expression

When compiling HLSL that uses a comma expression to initialize a local resource variable, DXC's SPIRV backend generates invalid SPIR-V:

fatal error: generated SPIR-V is invalid: Cannot load a runtime-sized array %13 = OpLoad %type_RWByteAddressBuffer %gBuf1

Repro:

RWByteAddressBuffer gBuf0 : register(u0); 
RWByteAddressBuffer gBuf1 : register(u1);

[numthreads(1,1,1)] void main() {  
RWByteAddressBuffer buf = (gBuf0, gBuf1);  
buf.Store(0, 42); 
}

Command:

dxc.exe -spirv -fspv-target-env=vulkan1.3 -T cs_6_0 -Fo out.spv repro.hlsl

DXC DXIL compiles and runs this correctly. DXC version: main (built from source).

Start by running the HLSL repro with dxc.exe using the provided SPIR-V command and confirm the invalid OpLoad diagnostic. Then trace the SPIR-V backend's handling of comma expressions when initializing a local resource, using the DXIL behavior as a comparison. Done means the repro produces valid SPIR-V and no longer reports that a runtime-sized array cannot be loaded.