diff --git a/libcxx/CMakeLists.txt b/libcxx/CMakeLists.txt
--- a/libcxx/CMakeLists.txt
+++ b/libcxx/CMakeLists.txt
@@ -55,16 +55,7 @@
    by users in their own code regardless of this option." OFF)
 option(LIBCXX_ENABLE_SHARED "Build libc++ as a shared library." ON)
 option(LIBCXX_ENABLE_STATIC "Build libc++ as a static library." ON)
-set(ENABLE_FILESYSTEM_DEFAULT ON)
-if (WIN32 AND NOT MINGW)
-  # Filesystem is buildable for windows, but it requires __int128 helper
-  # functions, that currently are provided by libgcc or compiler_rt builtins.
-  # These are available in MinGW environments, but not currently in MSVC
-  # environments.
-  set(ENABLE_FILESYSTEM_DEFAULT OFF)
-endif()
-option(LIBCXX_ENABLE_FILESYSTEM "Build filesystem as part of the main libc++ library"
-    ${ENABLE_FILESYSTEM_DEFAULT})
+option(LIBCXX_ENABLE_FILESYSTEM "Build filesystem as part of the main libc++ library" ON)
 option(LIBCXX_INCLUDE_TESTS "Build the libc++ tests." ${LLVM_INCLUDE_TESTS})
 option(LIBCXX_ENABLE_PARALLEL_ALGORITHMS "Enable the parallel algorithms library. This requires the PSTL to be available." OFF)
 option(LIBCXX_ENABLE_DEBUG_MODE
diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -655,7 +655,7 @@
 #    define _LIBCPP_PREFERRED_OVERLOAD __attribute__((__enable_if__(true, "")))
 #  endif
 
-#  ifndef __SIZEOF_INT128__
+#if !defined(__SIZEOF_INT128__) || defined(_MSC_VER)
 #    define _LIBCPP_HAS_NO_INT128
 #  endif
 
diff --git a/libcxx/utils/ci/run-buildbot b/libcxx/utils/ci/run-buildbot
--- a/libcxx/utils/ci/run-buildbot
+++ b/libcxx/utils/ci/run-buildbot
@@ -98,19 +98,10 @@
 }
 
 function generate-cmake-libcxx-win() {
-    # TODO: Clang-cl in MSVC configurations don't have access to compiler_rt
-    # builtins helpers for int128 division. See
-    # https://reviews.llvm.org/D91139#2429595 for a comment about longterm
-    # intent for handling the issue. In the meantime, define
-    # -D_LIBCPP_HAS_NO_INT128 (both when building the library itself and
-    # when building tests) to allow enabling filesystem for running tests,
-    # even if it uses a non-permanent ABI.
     generate-cmake-base \
           -DLLVM_ENABLE_RUNTIMES="libcxx" \
           -DCMAKE_C_COMPILER=clang-cl \
           -DCMAKE_CXX_COMPILER=clang-cl \
-          -DLIBCXX_ENABLE_FILESYSTEM=YES \
-          -DLIBCXX_EXTRA_SITE_DEFINES="_LIBCPP_HAS_NO_INT128" \
           "${@}"
 }