Index: cmake/platforms/WinMsvc.cmake
===================================================================
--- cmake/platforms/WinMsvc.cmake
+++ cmake/platforms/WinMsvc.cmake
@@ -8,6 +8,7 @@
 #    -DMSVC_BASE=/path/to/MSVC/system/libraries/and/includes
 #    -DWINSDK_BASE=/path/to/windows-sdk
 #    -DWINSDK_VER=windows sdk version folder name
+#    -DWINSDK_CASE_SENSITIVE=[YES|NO]
 #
 # LLVM_NATIVE_TOOLCHAIN:
 #   *Absolute path* to a folder containing the toolchain which will be used to
@@ -74,20 +75,22 @@
 #           kernel32.lib
 #           etc
 #
-# IMPORTANT: In order for this to work, you will need a valid copy of the Windows
-# SDK and C++ STL headers and libraries on your host.  Additionally, since the
-# Windows libraries and headers are not case-correct, you will need to have these
-# mounted in a case-insensitive mount.  This requires one command to set up.
+# WINSDK_CASE_SENSITIVE:
+#   The Windows SDK headers and libraries are not case-correct. You can mount
+#   the SDK in a case-insensitive mount to work around this. Run the following
+#   commands to set the mount up, and then copy the SDK headers and libraries to
+#   the winsdk.icase folder and use *that* folder as the path when configuring
+#   CMake.
 #
-# ~/src: mkdir winsdk
-# ~/src: mkdir winsdk.icase
-# ~/src: ciopfs winsdk/ winsdk.icase
+#   ~/src: mkdir winsdk
+#   ~/src: mkdir winsdk.icase
+#   ~/src: ciopfs winsdk/ winsdk.icase
 #
-# Now copy or otherwise install your headers and libraries to the winsdk.icase folder
-# and use *that* folder as the path when configuring CMake.
-#
-# TODO: We could also provide a CMake option -DUSE_ICASE_VFS_OVERLAY=ON/OFF that would
-# make this optional.  For now, we require ciopfs.
+#   Alternatively, you can set WINSDK_CASE_SENSITIVE to YES, in which case this
+#   toolchain file will assume the SDK is hosted on a case-sensitive filesystem,
+#   and will create a case-insensitive clang VFS overlay for the SDK headers and
+#   case-correcting symlinks for the libraries. WINSDK_CASE_SENSITIVE defaults
+#   to OFF; i.e., the default assumption is a case-insensitive mount.
 
 
 # When configuring CMake with a toolchain file against a top-level CMakeLists.txt,
@@ -106,6 +109,49 @@
   endif()
 endfunction()
 
+function(generate_winsdk_vfs_overlay winsdk_include_dir output_path)
+  set(include_dirs)
+  file(GLOB_RECURSE entries LIST_DIRECTORIES true "${winsdk_include_dir}/*")
+  foreach(entry ${entries})
+    if(IS_DIRECTORY "${entry}")
+      list(APPEND include_dirs "${entry}")
+    endif()
+  endforeach()
+
+  file(WRITE "${output_path}"  "version: 0\n")
+  file(APPEND "${output_path}" "case-sensitive: false\n")
+  file(APPEND "${output_path}" "roots:\n")
+
+  foreach(dir ${include_dirs})
+    file(GLOB headers RELATIVE "${dir}" "${dir}/*.h")
+    if(NOT headers)
+      continue()
+    endif()
+
+    file(APPEND "${output_path}" "  - name: \"${dir}\"\n")
+    file(APPEND "${output_path}" "    type: directory\n")
+    file(APPEND "${output_path}" "    contents:\n")
+
+    foreach(header ${headers})
+      file(APPEND "${output_path}" "      - name: \"${header}\"\n")
+      file(APPEND "${output_path}" "        type: file\n")
+      file(APPEND "${output_path}" "        external-contents: \"${dir}/${header}\"\n")
+    endforeach()
+  endforeach()
+endfunction()
+
+function(generate_winsdk_lib_symlinks winsdk_um_lib_dir output_dir)
+  execute_process(COMMAND "${CMAKE_COMMAND}" -E make_directory "${output_dir}")
+  file(GLOB libraries RELATIVE "${winsdk_um_lib_dir}" "${winsdk_um_lib_dir}/*")
+  foreach(library ${libraries})
+    string(TOLOWER "${library}" symlink_name)
+    execute_process(COMMAND "${CMAKE_COMMAND}"
+                            -E create_symlink
+                            "${winsdk_um_lib_dir}/${library}"
+                            "${output_dir}/${symlink_name}")
+  endforeach()
+endfunction()
+
 # FIXME: We should support target architectures other than x64
 set(CMAKE_SYSTEM_NAME Windows)
 set(CMAKE_SYSTEM_VERSION 10.0)
@@ -115,6 +161,7 @@
 init_user_prop(MSVC_BASE)
 init_user_prop(WINSDK_BASE)
 init_user_prop(WINSDK_VER)
+init_user_prop(WINSDK_CASE_SENSITIVE)
 
 set(MSVC_INCLUDE "${MSVC_BASE}/include")
 set(MSVC_LIB "${MSVC_BASE}/lib")
@@ -170,6 +217,18 @@
     -imsvc "${WINSDK_INCLUDE}/um"
     -imsvc "${WINSDK_INCLUDE}/winrt")
 
+if (WINSDK_CASE_SENSITIVE)
+  # Ensure all sub-configures use the top-level VFS overlay instead of generating their own.
+  init_user_prop(winsdk_vfs_overlay_path)
+  if(NOT winsdk_vfs_overlay_path)
+    set(winsdk_vfs_overlay_path "${CMAKE_BINARY_DIR}/winsdk_vfs_overlay.yaml")
+    generate_winsdk_vfs_overlay("${WINSDK_BASE}/Include/${WINSDK_VER}" "${winsdk_vfs_overlay_path}")
+    init_user_prop(winsdk_vfs_overlay_path)
+  endif()
+  list(APPEND COMPILE_FLAGS
+       -Xclang -ivfsoverlay -Xclang "${winsdk_vfs_overlay_path}")
+endif()
+
 string(REPLACE ";" " " COMPILE_FLAGS "${COMPILE_FLAGS}")
 
 # We need to preserve any flags that were passed in by the user. However, we
@@ -193,6 +252,18 @@
     -libpath:"${WINSDK_LIB}/ucrt/x64"
     -libpath:"${WINSDK_LIB}/um/x64")
 
+if(WINSDK_CASE_SENSITIVE)
+  # Ensure all sub-configures use the top-level symlinks dir instead of generating their own.
+  init_user_prop(winsdk_lib_symlinks_dir)
+  if(NOT winsdk_lib_symlinks_dir)
+    set(winsdk_lib_symlinks_dir "${CMAKE_BINARY_DIR}/winsdk_lib_symlinks")
+    generate_winsdk_lib_symlinks("${WINSDK_BASE}/Lib/${WINSDK_VER}/um/x64" "${winsdk_lib_symlinks_dir}")
+    init_user_prop(winsdk_lib_symlinks_dir)
+  endif()
+  list(APPEND LINK_FLAGS
+       -libpath:"${winsdk_lib_symlinks_dir}")
+endif()
+
 string(REPLACE ";" " " LINK_FLAGS "${LINK_FLAGS}")
 
 # See explanation for compiler flags above for the _INITIAL variables.