Modularize: Include some required headers

DenseMaps require the definition of a type to be available when using a
pointer to that type as a key to know how many bits are available for
tombstone/etc.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@317360 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed