Update status of clangd in the toolchain

We have clangd in the toolchain now, and it's sufficient to pass our
minimal tests.  Unfortunately it's hitting frequent assertion failures
during editing, so not marking as supported yet.

Author: benlangmuir

README.md

@@ -104,7 +104,7 @@ SourceKit-LSP is still in early development, so you may run into rough edges wit
 | Feature | Status | Notes |
 |---------|:------:|-------|
 | Swift | ✅ | |
-| C/C++/ObjC | ❌ | [clangd](https://clang.llvm.org/extra/clangd.html) is not available in the recommended toolchain. You can try out C/C++/ObjC support by building clangd from source and putting it in `PATH`.
+| C/C++/ObjC | ❌ | As of `swift-DEVELOPMENT-SNAPSHOT-2019-02-14-a` [clangd](https://clang.llvm.org/extra/clangd.html) is available but hitting frequent assertion failures.
 | Code completion | ✅ | |
 | Quick Help (Hover) | ✅ | |
 | Diagnostics | ✅ | |

Tests/SourceKitTests/LocalClangTests.swift

@@ -20,7 +20,7 @@ import XCTest
 final class LocalClangTests: XCTestCase {
 
   /// Whether to fail tests if clangd cannot be found.
-  static let requireClangd: Bool = false
+  static let requireClangd: Bool = true
 
   /// Whether clangd exists in the toolchain.
   var haveClangd: Bool = false