chore: ignore the prebuilt libs directory

libs/libLLVM-22.dll is a 155 MB downloadable artifact; keeping it out of the
index keeps clones and diffs small.

.gitignore

@@ -30,5 +30,7 @@ __pycache__/
 **/temp/
 **/__vpcbuild*__/
 **/_sha1_map.txt
+# Prebuilt binaries (LLVM DLLs, imported toolchains)
+/libs/
 # LSP signature cache
 .viperc-lsp-cache/