Tame clangd

Stop it from running on all CPUs;
Tell it not to index/build the build dirs

.clangd

@@ -0,0 +1,11 @@
+# Project clangd configuration.
+# Worker thread count (-j=1) is a clangd CLI flag; see .vscode/settings.json.
+
+CompileFlags:
+	CompilationDatabase: build-agent
+
+---
+If:
+	PathMatch: (build/.*|b/.*|build-[^/]+/.*|b-[^/]+/.*)
+Index:
+	Background: Skip

.vscode/settings.json

@@ -107,5 +107,10 @@
         "${workspaceFolder}/b/include",
         "/usr/include",
         "/usr/local/include"
+    ],
+    "clangd.arguments": [
+        "--enable-config",
+        "-j=1",
+        "--compile-commands-dir=${workspaceFolder}/build-agent"
     ]
 }