Fix the CAS tests on Windows when LLVM_ENABLE_ONDISK_CAS=OFF

[hjyamauchi]

Fix the CAS tests on Windows when LLVM_ENABLE_ONDISK_CAS=OFF The following tests now pass on Windows:

LLVM :: DebugInfo/CAS/AArch64/debug_line_and_info_dedupe.test
LLVM :: DebugInfo/CAS/AArch64/debug_unopt.ll
LLVM :: DebugInfo/CAS/AArch64/multiple_cus.ll
LLVM :: tools/llvm-cas-dump/basic_debug_test.ll
LLVM :: tools/llvm-cas-dump/enums_split.ll
LLVM :: tools/llvm-cas-dump/stats-dump.test
LLVM :: tools/llvm-cas-dump/types_split.ll
LLVM :: tools/llvm-cas-object-format/materialize-objects.s
LLVM-Unit :: CAS/./CASTests.exe/0/28
LLVM-Unit :: CAS/./CASTests.exe/19/28
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/BasicRealFSIteration
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/BasicRealFSRecursiveIteration
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/BasicRealFSRecursiveIterationNoPush
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/BrokenSymlinkRealFSRecursiveIteration
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/ExcludeFromTacking
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/Exists
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/MultipleWorkingDirs
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/TrackNewAccesses
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/TrackNewAccessesExists
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/TrackNewAccessesStack
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/caseSensitivityDir
LLVM-Unit :: CAS/./CASTests.exe/CachingOnDiskFileSystemTest/caseSensitivityFile
LLVM-Unit :: Support/./SupportTests.exe/SourceMgrTest/AddIncludedFile
LLVM-Unit :: Support/./SupportTests.exe/TreePathPrefixMapperTest/map
LLVM-Unit :: Support/./SupportTests.exe/TreePathPrefixMapperTest/mapInPlace
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectory/OnDisk
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectory/OnDisk_DisableRemoveOnSignal
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectory/OnDisk_DisableTemporaries
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectoryNested/OnDisk
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectoryNested/OnDisk_DisableRemoveOnSignal
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectoryNested/OnDisk_DisableTemporaries
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectoryNoImply/OnDisk
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectoryNoImply/OnDisk_DisableRemoveOnSignal
LLVM-Unit :: Support/./SupportTests.exe/VirtualOutput/BackendTest/KeepMissingDirectoryNoImply/OnDisk_DisableTemporaries

With LLVM_ENABLE_ONDISK_CAS=OFF, all the CAS tests pass.

Some tests are disabled for now because they work only when LVM_ENABLE_ONDISK_CAS=ON and the lack of support for creating symlinks in the FileSystem API on windows.

    With LLVM_ENABLE_ONDISK_CAS=ON, the following tests currently fail.
    LLVM :: tools/llvm-cas/ingest-blobs-casid.test
    LLVM :: tools/llvm-cas/ingest-remap.test
    LLVM :: tools/llvm-cas/ingest.test
    LLVM :: tools/llvm-cas/merge.test
    LLVM :: tools/llvm-cas/print-id.test
    LLVM-Unit :: CAS/./CASTests.exe/OnDiskCASTest/BlobsBigParallelMultiCAS
    LLVM-Unit :: CAS/./CASTests.exe/OnDiskCASTest/BlobsParallelMultiCAS
    LLVM-Unit :: CAS/./CASTests.exe/PluginCASTest/isMaterialized

Will work on fixing the tests with LVM_ENABLE_ONDISK_CAS=ON next.