[SPIRV] Fix asan failure (#138695)

When the DataLayout is destroyed, the memory backing `Offsets` is
released. This causes a use after free.

To fix it, I added a DataLayout varible that will not be destroyed until
after Offsets is used.

Fixes asan failure caused by
#135789

Author: s-perron

llvm/lib/Target/SPIRV/SPIRVGlobalRegistry.cpp

@@ -2062,8 +2062,8 @@ void SPIRVGlobalRegistry::updateAssignType(CallInst *AssignCI, Value *Arg,
 
 void SPIRVGlobalRegistry::addStructOffsetDecorations(
     Register Reg, StructType *Ty, MachineIRBuilder &MIRBuilder) {
-  ArrayRef<TypeSize> Offsets =
-      DataLayout().getStructLayout(Ty)->getMemberOffsets();
+  DataLayout DL;
+  ArrayRef<TypeSize> Offsets = DL.getStructLayout(Ty)->getMemberOffsets();
   for (uint32_t I = 0; I < Ty->getNumElements(); ++I) {
     buildOpMemberDecorate(Reg, MIRBuilder, SPIRV::Decoration::Offset, I,
                           {static_cast<uint32_t>(Offsets[I])});