rust_analyzer_helix.toml: add library/ manifest

Author: tshepang

src/etc/rust_analyzer_helix.toml

@@ -4,8 +4,9 @@ linkedProjects = [
     "src/tools/x/Cargo.toml",
     "src/bootstrap/Cargo.toml",
     "src/tools/rust-analyzer/Cargo.toml",
+    "library/Cargo.toml",
     "compiler/rustc_codegen_cranelift/Cargo.toml",
-    "compiler/rustc_codegen_gcc/Cargo.toml"
+    "compiler/rustc_codegen_gcc/Cargo.toml",
 ]
 
 [language-server.rust-analyzer.config.check]