[TableGen] Use FoldingSets instead of DenseMaps to unique UnOpInit, BinOpInit and TernOpInit. This remove the memory needed to store the key for the DenseMap. NFC

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@258071 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed