[gn] Move Features.inc to clangd, create a config for it

[phosek]

Summary

ClangdLSPServer and clangd unittests now include Features.inc so we
need to append the target_gen_dir that contains it to their
include_dirs. To do so, we use a public config that's applied to
any target that depends on the features one.

[thakis]

Thanks!

[thakis]

Looks like this doesn't build:

[1/1] Regenerating ninja files
FAILED: build.ninja
../../llvm/utils/gn/bin/mac-amd64/gn --root=../.. -q --dotfile=../../llvm/utils/gn/.gn gen .
ERROR Unresolved dependencies.
//clang-tools-extra/clangd:clangd(//llvm/utils/gn/build/toolchain:unix)
  needs //clang-tools-extra/clangd/tool:features(//llvm/utils/gn/build/toolchain:unix)

[thakis]

llvm/trunk/utils/gn/secondary/clang-tools-extra/clangd/BUILD.gn

22 ↗

(On Diff #195983)

Ah, you didn't remove this line. Fixing; but please try your changes locally before landing :)

llvm/utils/gn/secondary/clang-tools-extra/clangd/BUILD.gn

deps = [
     "//clang/lib/Tooling",
     "//clang/lib/Tooling/Core",
     "//clang/lib/Tooling/Inclusions",
     "//clang/lib/Tooling/Refactoring",
     "//llvm/lib/Support",
     "//llvm/utils/gn/build/libs/atomic",
     "//llvm/utils/gn/build/libs/pthread",
   ]
-  include_dirs = [ "." ]
+  include_dirs = [
+    ".",
+    get_label_info("//clang-tools-extra/clangd/tool:features", "target_gen_dir"),
+  ]
   sources = [
     "AST.cpp",
     "Cancellation.cpp",
     "ClangdLSPServer.cpp",
     "ClangdServer.cpp",
     "ClangdUnit.cpp",
     "CodeComplete.cpp",
     "CodeCompletionStrings.cpp",

llvm/utils/gn/secondary/clang-tools-extra/unittests/clangd/BUILD.gn

deps = [
     "//clang/lib/Sema",
     "//clang/lib/Serialization",
     "//clang/lib/Tooling",
     "//clang/lib/Tooling/Core",
     "//clang/lib/Tooling/Inclusions",
     "//llvm/lib/Support",
     "//llvm/lib/Testing/Support",
   ]
-  include_dirs = [ "//clang-tools-extra/clangd" ]
+  include_dirs = [
+    "//clang-tools-extra/clangd",
+    get_label_info("//clang-tools-extra/clangd/tool:features", "target_gen_dir"),
+  ]
   sources = [
     "Annotations.cpp",
     "BackgroundIndexTests.cpp",
     "CancellationTests.cpp",
     "ClangdTests.cpp",
     "ClangdUnitTests.cpp",
     "CodeCompleteTests.cpp",
     "CodeCompletionStringsTests.cpp",