chore: isolate Zed clangd from Watcom headers

.clangd

@@ -0,0 +1,6 @@
+# yaml-language-server: $schema=https://json.schemastore.org/clangd.json
+CompileFlags:
+  Add:
+    - -xc
+    - -std=c89
+    - -Ifec/src

.zed/settings.json

@@ -0,0 +1,11 @@
+{
+  "lsp": {
+    "clangd": {
+      "binary": {
+        "env": {
+          "INCLUDE": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2019\\BuildTools\\VC\\Tools\\MSVC\\14.29.30133\\include;C:\\Program Files (x86)\\Windows Kits\\10\\Include\\10.0.19041.0\\ucrt;C:\\Program Files (x86)\\Windows Kits\\10\\Include\\10.0.19041.0\\shared;C:\\Program Files (x86)\\Windows Kits\\10\\Include\\10.0.19041.0\\um;C:\\Program Files (x86)\\Windows Kits\\10\\Include\\10.0.19041.0\\winrt"
+        }
+      }
+    }
+  }
+}