Incremental static-library builds retain removed source objects

[alz458]

Incremental static-library builds retain removed source objects

When a source is removed from a static-library target and deleted from disk, rebuilding can retain its old object in the archive. An application that references its function can still link, while a clean build fails.

Reproduced on macOS with Python 3.13 at commit 76970c97c67f3c14c627e4420c0a3f02b6de66ed:

1. Define a static library containing keep.c and removed.c, and an executable that depends on the library and calls a function in removed.c.
2. Build successfully.
3. Delete removed.c and remove it from the target's sources.
4. Rebuild in the existing build directory: the executable still links.
5. Build into a fresh directory: linking correctly fails because the function is missing.

Expected: both builds reject the reference to the removed function.
Actual: ar t shows removed.o still in the incrementally rebuilt archive.

The generated ar rcs $out $in command updates supplied members but retains omitted members. Recreating the archive when its Ninja edge runs resolves this inconsistency.