[CfToHandshake] Do not replace the same value twice

[Jiahui17]

In CfToHandshake, we are calling inlineBlockBefore after replaceAllUsesWith. Internally, inlineBlockBefore calls ConversionPatternRewriterImpl::replaceOp.

dynamatic/lib/Conversion/CfToHandshake/CfToHandshake.cpp

Lines 1045 to 1050 in 13d273d

	for (BlockArgument blockArg : block.getArguments()) {
	Value mergeRes = argReplacements.at(blockArg);
	replacements.push_back(mergeRes);
	rewriter.replaceAllUsesWith(blockArg, mergeRes);
	}
	rewriter.inlineBlockBefore(&block, lastOp, replacements);

In the latest LLVM, ConversionPatternRewriterImpl::replaceOp asserts that the value that's being replaced must not have already been replaced, which is not true in the logic above.

To fix this, when constructing MC/LSQ, use the merge outputs directly rather than the block arguments for GAs and the number of stores. This omits the need to call replaceAllUsesWith

[Jiahui17]

I pulled this out of #654. Does this still break FTD? @AyaElAkhras ?