[mlir] Add SmallVector sizes

[tpopp]

Summary

This is a temporary fix until figuring out how to correct the forward
declare in mlir/include/mlir/Support/LLVM.h

[mehdi_amini]

What is the problem you're trying to solve here?

mlir/lib/Dialect/LLVMIR/IR/LLVMDialect.cpp

 // LLVM::SwitchOp
 //===----------------------------------------------------------------------===//
 
 void SwitchOp::build(OpBuilder &builder, OperationState &result, Value value,
                      Block *defaultDestination, ValueRange defaultOperands,
                      ArrayRef<int32_t> caseValues, BlockRange caseDestinations,
                      ArrayRef<ValueRange> caseOperands,
                      ArrayRef<int32_t> branchWeights) {
-  SmallVector<Value> flattenedCaseOperands;
-  SmallVector<int32_t> caseOperandOffsets;
+  SmallVector<Value, 8> flattenedCaseOperands;
+  SmallVector<int32_t, 8> caseOperandOffsets;
   int32_t offset = 0;
   for (ValueRange operands : caseOperands) {
     flattenedCaseOperands.append(operands.begin(), operands.end());
     caseOperandOffsets.push_back(offset);
     offset += operands.size();
   }
   ElementsAttr caseValuesAttr;
   if (!caseValues.empty())

 /// <cases> ::= integer `:` bb-id (`(` ssa-use-and-type-list `)`)?
 ///             ( `,` integer `:` bb-id (`(` ssa-use-and-type-list `)`)? )?
 static ParseResult
 parseSwitchOpCases(OpAsmParser &parser, ElementsAttr &caseValues,
                    SmallVectorImpl<Block *> &caseDestinations,
                    SmallVectorImpl<OpAsmParser::OperandType> &caseOperands,
                    SmallVectorImpl<Type> &caseOperandTypes,
                    ElementsAttr &caseOperandOffsets) {
-  SmallVector<int32_t> values;
-  SmallVector<int32_t> offsets;
+  SmallVector<int32_t, 8> values;
+  SmallVector<int32_t, 8> offsets;
   int32_t value, offset = 0;
   do {
     OptionalParseResult integerParseResult = parser.parseOptionalInteger(value);
     if (values.empty() && !integerParseResult.hasValue())
       return success();
 
     if (!integerParseResult.hasValue() || integerParseResult.getValue())
       return failure();
     values.push_back(value);
 
     Block *destination;
-    SmallVector<OpAsmParser::OperandType> operands;
+    SmallVector<OpAsmParser::OperandType, 8> operands;
     if (parser.parseColon() || parser.parseSuccessor(destination))
       return failure();
     if (!parser.parseOptionalLParen()) {
       if (parser.parseRegionArgumentList(operands) ||
           parser.parseColonTypeList(caseOperandTypes) || parser.parseRParen())
         return failure();
     }
     caseDestinations.push_back(destination);