[llvm-pdbdump] Only build the TypeDatabase if necessary.

[llvm-pdbdump] Only build the TypeDatabase if necessary.

Building the type database is expensive, and can take multiple
minutes for large PDBs.  But we only need it in certain cases
depending on what command line options are specified.  So only
build it when we know we're about to need it.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302204 91177308-0d34-0410-b5e6-96231b3b80d8