Add Experimental Differentiation build (#998)

Author: Steelskin

.github/workflows/swift-toolchain.yml

@@ -2704,6 +2704,69 @@ jobs:
         run: |
           cmake --build ${{ github.workspace }}/BinaryCache/ExperimentalObservation --target install
 
+      - name: Configure Experimental Differentiation
+        if: matrix.os != 'Android' || inputs.build_android
+        run: |
+          $CLANG = cygpath -m "${{ github.workspace }}/BinaryCache/Library/Developer/Toolchains/${{ inputs.swift_version }}+Asserts/usr/bin/clang.exe"
+          $CLANGXX = cygpath -m "${{ github.workspace }}/BinaryCache/Library/Developer/Toolchains/${{ inputs.swift_version }}+Asserts/usr/bin/clang++.exe"
+          $CLANG_CL = cygpath -m "${{ github.workspace }}/BinaryCache/Library/Developer/Toolchains/${{ inputs.swift_version }}+Asserts/usr/bin/clang-cl.exe"
+          $SWIFTC = cygpath -m "${{ github.workspace }}/BinaryCache/Library/Developer/Toolchains/${{ inputs.swift_version }}+Asserts/usr/bin/swiftc.exe"
+          $SwiftFlags = "${{ matrix.swiftflags }}"
+
+          if ("${{ matrix.os }}" -eq "Android") {
+            # Used by matrix definitions.
+            $NDKPATH = cygpath -m ${{ steps.setup-ndk.outputs.ndk-path }}
+          }
+
+          if ("${{ matrix.os }}" -eq "Windows") {
+            $WINDOWS_VFS_OVERLAY = cygpath -m "${{ github.workspace }}/BinaryCache/swift/stdlib/windows-vfs-overlay.yaml"
+            $SwiftResourceDir = cygpath -m "${{ github.workspace }}/BinaryCache/Library/Developer/Platforms/Windows.platform/Developer/SDKs/Windows.sdk/usr/lib/swift"
+            $SwiftFlags += " -vfsoverlay ${WINDOWS_VFS_OVERLAY}"
+            $SwiftFlags += " -strict-implicit-module-context"
+            $SwiftFlags += " -Xcc -Xclang -Xcc -fbuiltin-headers-in-system-modules"
+            $SwiftFlags += " -resource-dir $SwiftResourceDir"
+            $SwiftFlags += " -L $SwiftResourceDir/windows"
+          } elseif ("${{ matrix.os }}" -eq "Android") {
+            $SwiftResourceDir = cygpath -m "${{ github.workspace }}/BinaryCache/Library/Developer/Platforms/Android.platform/Developer/SDKs/Android.sdk/usr/lib/swift"
+            $SwiftFlags += " -sdk $NDKPATH/toolchains/llvm/prebuilt/windows-x86_64/sysroot"
+            $SwiftFlags += " -resource-dir $SwiftResourceDir"
+            $SwiftFlags += " -L $SwiftResourceDir/android"
+          }
+
+          cmake -B ${{ github.workspace }}/BinaryCache/ExperimentalDifferentiation `
+                -D CMAKE_BUILD_TYPE=Release `
+                -D CMAKE_C_COMPILER=${{ matrix.gnu-cc }} `
+                -D CMAKE_C_COMPILER_LAUNCHER=sccache `
+                -D CMAKE_C_COMPILER_TARGET=${{ matrix.triple }} `
+                -D CMAKE_C_FLAGS="${{ matrix.gnu-cflags }}" `
+                -D CMAKE_CXX_COMPILER=${{ matrix.gnu-cxx }} `
+                -D CMAKE_CXX_COMPILER_LAUNCHER=sccache `
+                -D CMAKE_CXX_COMPILER_TARGET=${{ matrix.triple }} `
+                -D CMAKE_CXX_FLAGS="${{ matrix.gnu-cxxflags }}" `
+                -D CMAKE_Swift_COMPILER=${SWIFTC} `
+                -D CMAKE_Swift_COMPILER_TARGET=${{ matrix.triple_no_api_level }} `
+                -D CMAKE_Swift_FLAGS="${SwiftFlags}" `
+                -D CMAKE_Swift_COMPILER_WORKS=YES `
+                -D CMAKE_Swift_COMPILER_USE_OLD_DRIVER=YES `
+                -D BUILD_SHARED_LIBS=NO `
+                -D CMAKE_INSTALL_PREFIX=${{ github.workspace }}/BuildRoot/Library/Developer/Platforms/${{ matrix.os }}.platform/Developer/SDKs/${{ matrix.os }}Experimental.sdk/usr `
+                -D CMAKE_FIND_PACKAGE_PREFER_CONFIG=YES `
+                -D CMAKE_STATIC_LIBRARY_PREFIX_Swift="lib" `
+                ${{ matrix.gnu-linker_flags }} `
+                ${{ matrix.extra_flags }} `
+                -G Ninja `
+                -S ${{ github.workspace }}/SourceCache/swift/Runtimes/Supplemental/Differentiation `
+                -D SwiftCore_DIR=${{ github.workspace }}/BinaryCache/ExperimentalRuntime/cmake/SwiftCore `
+                -D SwiftOverlay_DIR=${{ github.workspace }}/BinaryCache/ExperimentalOverlay/cmake/SwiftOverlay
+      - name: Build Experimental Differentiation
+        if: matrix.os != 'Android' || inputs.build_android
+        run: |
+          cmake --build ${{ github.workspace }}/BinaryCache/ExperimentalDifferentiation
+      - name: Install Experimental Differentiation
+        if: matrix.os != 'Android' || inputs.build_android
+        run: |
+          cmake --build ${{ github.workspace }}/BinaryCache/ExperimentalDifferentiation --target install
+
       - name: Configure Experimental Dispatch
         if: matrix.os != 'Android' || inputs.build_android
         run: |