Improve compilation database for agents. (#7790)

Remove claim from script that it takes minutes; this caused Claude to
decide to not run it. It only takes a few seconds these days. Add note
in toolchain development skill that lints won't be accurate if the
compilation database is outdated.

Assisted-by: Claude Opus 5 via Antigravity

.agents/skills/toolchain_development/SKILL.md

@@ -158,3 +158,8 @@ operations, inspect target LLVM ADT class APIs:
 8.  **Redundant bounds calculations**: Avoid repeating calculations of complex
     boundary estimations (such as lower and upper bound estimations). Refactor
     the logic to calculate unified values once, preserving compactness.
+9.  **Trusting stale `clangd` diagnostics**: In-editor diagnostics are only as
+    good as `compile_commands.json`. If it predates a newly added file, `clangd`
+    falls back to a default command and reports nonsense, such as missing
+    standard headers or "no member named `None`". Regenerate it with
+    `./scripts/create_compdb.py`, which only takes a few seconds.

scripts/create_compdb.py

@@ -196,10 +196,7 @@ def main() -> None:
         bazel, args.alsologtostderr, args.dump_files, args.extra_bazel_flag
     )
 
-    print(
-        "Generating compile_commands.json (may take a few minutes)...",
-        flush=True,
-    )
+    print("Generating compile_commands.json...", flush=True)
     subprocess.run(
         [
             bazel,