Add basic clangd

lsp/clangd-lsp.lua

@@ -0,0 +1,25 @@
+return {
+  filetypes = { "c", "cpp", "h" },
+  cmd = { "clangd-18", '--background-index', '--clang-tidy', '--log=verbose',
+        "--header-insertion=iwyu",
+        "--completion-style=detailed",
+        "--function-arg-placeholders",
+        "--fallback-style=llvm",
+      },
+  root_markers = {
+    "compile_commands.json",
+    "compile_flags.txt",
+    "configure.ac", -- AutoTools
+    "Makefile",
+    "configure.ac",
+    "configure.in",
+    "config.h.in",
+    "meson.build",
+    "meson_options.txt",
+    "build.ninja",
+    ".git",
+  },
+  init_options = {
+    clangdFileStatus = true,
+  },
+}