Build PDB file for Windows (#1678)

This allows dumping human-readable backtrace symbols with line numbers.

Also limit the maximum link jobs to 1 to avoid OOM in CI.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -17,6 +17,9 @@ If you can, provide a minimal chunk of code that shows the problem (either inlin
 Please attach the clangd stderr log if you can. (Usually available from the editor)
 If possible, run with `--log=verbose` - note that the logs will include the contents of open files!
 If this is a crash, try to put `llvm-symbolizer` on your PATH per the troubleshooting instructions.
+(If you're using Windows, place the associated PDB file (debug symbols) in the same directory as
+clangd.exe and rerun again. For official releases, download symbols from the
+[release page](https://github.com/clangd/clangd/releases).)
 
 **System information**
 

.github/workflows/autobuild.yaml

@@ -156,6 +156,8 @@ jobs:
             "-DCMAKE_CXX_COMPILER=cl"
             "-DLLVM_ENABLE_ZLIB=OFF"
             "-DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded"
+            "-DLLVM_ENABLE_PDB=ON"
+            "-DLLVM_PARALLEL_LINK_JOBS=1"
           grpc_cmake: >-
             "-DgRPC_MSVC_STATIC_RUNTIME=ON"
           binary_extension: ".exe"
@@ -309,6 +311,12 @@ jobs:
         ${{ env.CLANGD_DIR }}/LICENSE.TXT
         ${{ env.CLANGD_DIR }}/bin/clangd${{ matrix.config.binary_extension }}
         ${{ env.CLANGD_DIR }}/lib/clang
+    - name: Archive clangd PDB symbols
+      if: matrix.config.name == 'windows'
+      run: >
+        7z a clangd-pdb.7z -t7z -m0=LZMA2
+        ${{ env.CLANGD_DIR }}/LICENSE.TXT
+        ${{ env.CLANGD_DIR }}/bin/clangd.pdb
     - name: Archive indexing-tools
       run: >
         7z a indexing-tools.zip
@@ -326,6 +334,16 @@ jobs:
         asset_name: clangd-${{ matrix.config.name }}-${{ env.TAG_NAME }}.zip
         asset_path: clangd.zip
         asset_content_type: application/zip
+    - name: Upload clangd PDB asset
+      if: matrix.config.name == 'windows'
+      uses: actions/upload-release-asset@v1.0.1
+      env:
+        GITHUB_TOKEN: ${{ secrets.RELEASE_TOKEN }}
+      with:
+        upload_url: ${{ env.UPLOAD_URL }}
+        asset_name: clangd-${{ matrix.config.name }}-${{ env.TAG_NAME }}-debug-symbols.7z
+        asset_path: clangd-pdb.7z
+        asset_content_type: application/zip
     - name: Upload indexing-tools asset
       uses: actions/upload-release-asset@v1.0.1
       env: