[MLIR] Add forgotten directory Support to unittests cmake

[MLIR] Add forgotten directory Support to unittests cmake

The Support directory was removed from the unittests cmake when the directory
was removed in 204c3b551626a925dfdc3822a6f240bdc8ef5d3a. Subsequent commits
added the directory back but seem to have missed adding it back to the cmake.

This patch also removes MLIRSupportIndentedStream from the list of linked
libraries to avoid an ODR violation (it's already part of MLIRSupport which
is also being linked here). Otherwise ASAN complains:

```
=================================================================
==102592==ERROR: AddressSanitizer: odr-violation (0x7fbdf214eee0):
  [1] size=120 'vtable for mlir::raw_indented_ostream' /home/arjun/llvm-project/mlir/lib/Support/IndentedOstream.cpp
  [2] size=120 'vtable for mlir::raw_indented_ostream' /home/arjun/llvm-project/mlir/lib/Support/IndentedOstream.cpp
These globals were registered at these points:
  [1]:
    #0 0x28a71d in __asan_register_globals (/home/arjun/llvm-project/build/tools/mlir/unittests/Support/MLIRSupportTests+0x28a71d)
    #1 0x7fbdf214a61b in asan.module_ctor (/home/arjun/llvm-project/build/lib/libMLIRSupportIndentedOstream.so.14git+0x661b)

  [2]:
    #0 0x28a71d in __asan_register_globals (/home/arjun/llvm-project/build/tools/mlir/unittests/Support/MLIRSupportTests+0x28a71d)
    #1 0x7fbdf2061c4b in asan.module_ctor (/home/arjun/llvm-project/build/lib/libMLIRSupport.so.14git+0x11bc4b)

==102592==HINT: if you don't care about these errors you may set ASAN_OPTIONS=detect_odr_violation=0
SUMMARY AddressSanitizer: odr-violation: global 'vtable for mlir::raw_indented_ostream' at /home/arjun/llvm-project/mlir/lib/Support/IndentedOstream.cpp
==102592==ABORTING
```

This patch also fixes a build issue with `DebugAction::classof` under Windows.

This commit re-lands this patch, which was previously reverted in
2132906836cf0618e76485c67a60305bf1557ffc due to a buildbot failure that
turned out to be because of a flaky test.

Reviewed By: jpienaar

Differential Revision: https://reviews.llvm.org/D116027