[TableGen] Use StringMap instead of DenseMap<StringRef> to unique CodeInit and StringInit objects. Override the allocator to keep using the BumpPtrAllocator. NFCI

StringMap is better suited to mapping strings than a DenseMap.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@304178 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed