fix update llvm lld build command

src/backend/updating-llvm.md

@@ -91,6 +91,7 @@ so let's go through each in detail.
    Some commands you should execute are:
 
    * `./x build src/llvm-project` - test that LLVM still builds
+   * `./x build src/llvm-project/lld` - same for LLD
    * `./x build` - build the rest of rustc
 
    You'll likely need to update [`llvm-wrapper/*.cpp`][`llvm-wrapper`]
@@ -147,17 +148,17 @@ so let's go through each in detail.
    others interested in trying out the new LLVM can benefit from work you've done
    to update the C++ bindings.
 
-3. Over the next few months,
+6. Over the next few months,
    LLVM will continually push commits to its `release/a.b` branch.
    We will often want to have those bug fixes as well.
    The merge process for that is to use `git merge` itself to merge LLVM's
    `release/a.b` branch with the branch created in step 2.
    This is typically
    done multiple times when necessary while LLVM's release branch is baking.
 
-4. LLVM then announces the release of version `a.b`.
+7. LLVM then announces the release of version `a.b`.
 
-5. After LLVM's official release,
+8. After LLVM's official release,
    we follow the process of creating a new branch on the
    rust-lang/llvm-project repository again,
    this time with a new date.