Disable docs for compiler-builtins and sysroot

Bootstrap already had a manual doc filter for the `sysroot` crate, but
other library crates keep themselves out of the public docs by setting
`[lib] doc = false` in their manifest. This seems like a better solution
to hide `compiler-builtins` docs, and removes the `sysroot` hack too.

(cherry picked from commit 87e7539fcd)

library/compiler-builtins/compiler-builtins/Cargo.toml

@@ -19,6 +19,8 @@ links = "compiler-rt"
 bench = false
 doctest = false
 test = false
+# make sure this crate isn't included in public standard library docs
+doc = false
 
 [dependencies]
 core = { path = "../../core", optional = true }

library/sysroot/Cargo.toml

@@ -5,6 +5,10 @@ name = "sysroot"
 version = "0.0.0"
 edition = "2024"
 
+[lib]
+# make sure this crate isn't included in public standard library docs
+doc = false
+
 # this is a dummy crate to ensure that all required crates appear in the sysroot
 [dependencies]
 proc_macro = { path = "../proc_macro", public = true }

src/bootstrap/src/core/build_steps/doc.rs

@@ -734,10 +734,6 @@ fn doc_std(
     }
 
     for krate in requested_crates {
-        if krate == "sysroot" {
-            // The sysroot crate is an implementation detail, don't include it in public docs.
-            continue;
-        }
         cargo.arg("-p").arg(krate);
     }