Revert "[CAS] Add MappedFileRegionArena (#114099)"

This reverts commit f9cd2ee.

Author: ilovepi

llvm/CMakeLists.txt

@@ -878,7 +878,6 @@ option (LLVM_ENABLE_SPHINX "Use Sphinx to generate llvm documentation." OFF)
 option (LLVM_ENABLE_OCAMLDOC "Build OCaml bindings documentation." ON)
 option (LLVM_ENABLE_BINDINGS "Build bindings." ON)
 option (LLVM_ENABLE_TELEMETRY "Enable the telemetry library. If set to OFF, library cannot be enabled after build (eg., at runtime)" ON)
-option (LLVM_ENABLE_ONDISK_CAS "Build OnDiskCAS." ON)
 
 set(LLVM_INSTALL_DOXYGEN_HTML_DIR "${CMAKE_INSTALL_DOCDIR}/llvm/doxygen-html"
     CACHE STRING "Doxygen-generated HTML documentation install directory")

llvm/include/llvm/CAS/MappedFileRegionArena.h

@@ -146,7 +146,4 @@
    coverage bugs, and to 0 otherwise. */
 #cmakedefine01 LLVM_ENABLE_DEBUGLOC_TRACKING_ORIGIN
 
-/* Define to 1 to enable LLVM OnDisk Content Addressable Storage */
-#cmakedefine01 LLVM_ENABLE_ONDISK_CAS
-
 #endif

llvm/include/llvm/Config/llvm-config.h.cmake

@@ -410,11 +410,6 @@ LLVM_ABI std::error_code copy_file(const Twine &From, int ToFD);
 ///          platform-specific error_code.
 LLVM_ABI std::error_code resize_file(int FD, uint64_t Size);
 
-/// Resize path to size with sparse files explicitly enabled. It uses
-/// FSCTL_SET_SPARSE On Windows. This is the same as resize_file on
-/// non-Windows
-LLVM_ABI std::error_code resize_file_sparse(int FD, uint64_t Size);
-
 /// Resize \p FD to \p Size before mapping \a mapped_file_region::readwrite. On
 /// non-Windows, this calls \a resize_file(). On Windows, this is a no-op,
 /// since the subsequent mapping (via \c CreateFileMapping) automatically

llvm/include/llvm/Support/FileSystem.h

@@ -3,9 +3,7 @@ add_llvm_component_library(LLVMCAS
   ActionCaches.cpp
   BuiltinCAS.cpp
   InMemoryCAS.cpp
-  MappedFileRegionArena.cpp
   ObjectStore.cpp
-  OnDiskCommon.cpp
 
   ADDITIONAL_HEADER_DIRS
   ${LLVM_MAIN_INCLUDE_DIR}/llvm/CAS