docs(build-rs): Fix broken intra-doc links (#15810)

### What does this PR try to resolve?

Unblock CI

### How to test and review this PR?

### Notes

These were caught with the latest nightly

This was pulled from #15800

Author: weihanglo

crates/build-rs/src/output.rs

@@ -119,6 +119,8 @@ pub fn rustc_link_arg_bins(flag: &str) {
 /// The `rustc-link-arg-tests` instruction tells Cargo to pass the
 /// [`-C link-arg=FLAG` option][link-arg] to the compiler, but only when building
 /// a tests target.
+///
+/// [link-arg]: https://doc.rust-lang.org/rustc/codegen-options/index.html#link-arg
 #[track_caller]
 pub fn rustc_link_arg_tests(flag: &str) {
     if flag.contains([' ', '\n']) {
@@ -130,6 +132,8 @@ pub fn rustc_link_arg_tests(flag: &str) {
 /// The `rustc-link-arg-examples` instruction tells Cargo to pass the
 /// [`-C link-arg=FLAG` option][link-arg] to the compiler, but only when building
 /// an examples target.
+///
+/// [link-arg]: https://doc.rust-lang.org/rustc/codegen-options/index.html#link-arg
 #[track_caller]
 pub fn rustc_link_arg_examples(flag: &str) {
     if flag.contains([' ', '\n']) {
@@ -141,6 +145,8 @@ pub fn rustc_link_arg_examples(flag: &str) {
 /// The `rustc-link-arg-benches` instruction tells Cargo to pass the
 /// [`-C link-arg=FLAG` option][link-arg] to the compiler, but only when building
 /// a benchmark target.
+///
+/// [link-arg]: https://doc.rust-lang.org/rustc/codegen-options/index.html#link-arg
 #[track_caller]
 pub fn rustc_link_arg_benches(flag: &str) {
     if flag.contains([' ', '\n']) {

src/cargo/core/compiler/rustdoc.rs

@@ -243,7 +243,7 @@ pub fn add_root_urls(
 }
 
 /// Adds unstable flag [`--output-format`][1] to the given `rustdoc`
-/// invocation. This is for unstable feature [`-Zunstable-features`].
+/// invocation. This is for unstable feature `-Zunstable-features`.
 ///
 /// [1]: https://doc.rust-lang.org/nightly/rustdoc/unstable-features.html?highlight=output-format#-w--output-format-output-format
 pub fn add_output_format(

src/cargo/util/context/mod.rs

@@ -1982,7 +1982,7 @@ impl GlobalContext {
         Ok(())
     }
 
-    /// Returns a list of [target.'`cfg()`'] tables.
+    /// Returns a list of `target.'cfg()'` tables.
     ///
     /// The list is sorted by the table name.
     pub fn target_cfgs(&self) -> CargoResult<&Vec<(String, TargetCfgConfig)>> {