[clangd] Fix Windows build when remote index is enabled.

CMake log:
```
CMake Error at D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:823 (add_executable):
  Target "clangd" links to target "Threads::Threads" but the target was not
  found.  Perhaps a find_package() call is missing for an IMPORTED target, or
  an ALIAS target is missing?
Call Stack (most recent call first):
  D:/llvm-project/clang/cmake/modules/AddClang.cmake:150 (add_llvm_executable)
  D:/llvm-project/clang/cmake/modules/AddClang.cmake:160 (add_clang_executable)
  D:/llvm-project/clang-tools-extra/clangd/tool/CMakeLists.txt:4 (add_clang_tool)

CMake Error at D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:821 (add_executable):
  Target "ClangdTests" links to target "Threads::Threads" but the target was
  not found.  Perhaps a find_package() call is missing for an IMPORTED
  target, or an ALIAS target is missing?
Call Stack (most recent call first):
  D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:1417 (add_llvm_executable)
  D:/llvm-project/clang-tools-extra/clangd/unittests/CMakeLists.txt:32 (add_unittest)

CMake Error at D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:527 (add_library):
  Target "RemoteIndexProtos" links to target "Threads::Threads" but the
  target was not found.  Perhaps a find_package() call is missing for an
  IMPORTED target, or an ALIAS target is missing?
Call Stack (most recent call first):
  D:/llvm-project/clang/cmake/modules/AddClang.cmake:103 (llvm_add_library)
  D:/llvm-project/llvm/cmake/modules/FindGRPC.cmake:105 (add_clang_library)
  D:/llvm-project/clang-tools-extra/clangd/index/remote/CMakeLists.txt:2 (generate_grpc_protos)

CMake Error at D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:527 (add_library):
  Target "clangdRemoteIndex" links to target "Threads::Threads" but the
  target was not found.  Perhaps a find_package() call is missing for an
  IMPORTED target, or an ALIAS target is missing?
Call Stack (most recent call first):
  D:/llvm-project/clang/cmake/modules/AddClang.cmake:103 (llvm_add_library)
  D:/llvm-project/clang-tools-extra/clangd/index/remote/CMakeLists.txt:11 (add_clang_library)

CMake Error at D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:527 (add_library):
  Target "clangdRemoteMarshalling" links to target "Threads::Threads" but the
  target was not found.  Perhaps a find_package() call is missing for an
  IMPORTED target, or an ALIAS target is missing?
Call Stack (most recent call first):
  D:/llvm-project/clang/cmake/modules/AddClang.cmake:103 (llvm_add_library)
  D:/llvm-project/clang-tools-extra/clangd/index/remote/marshalling/CMakeLists.txt:1 (add_clang_library)

CMake Error at D:/llvm-project/llvm/cmake/modules/AddLLVM.cmake:823 (add_executable):
  Target "clangd-index-server" links to target "Threads::Threads" but the
  target was not found.  Perhaps a find_package() call is missing for an
  IMPORTED target, or an ALIAS target is missing?
```

Reviewed By: kbobyrev

Differential Revision: https://reviews.llvm.org/D86052

diff --git a/llvm/cmake/modules/FindGRPC.cmake b/llvm/cmake/modules/FindGRPC.cmake
index b7fafb2..3e33c2e 100644 (file)
--- a/llvm/cmake/modules/FindGRPC.cmake
+++ b/llvm/cmake/modules/FindGRPC.cmake
@@ -1,5 +1,6 @@
 # FIXME(kirillbobyrev): Check if gRPC and Protobuf headers can be included at
 # configure time.
+find_package(Threads REQUIRED)
 if (GRPC_INSTALL_PATH)
   # This setup requires gRPC to be built from sources using CMake and installed
   # to ${GRPC_INSTALL_PATH} via -DCMAKE_INSTALL_PREFIX=${GRPC_INSTALL_PATH}.