Update more occurrences of system llvm link

Author: Stupremee

src/building/new-target.md

@@ -28,7 +28,7 @@ If you have a local LLVM checkout that is already built, you *may* be
 able to configure Rust to treat your build as the [system
 LLVM][sysllvm] to avoid redundant builds.
 
-[sysllvm]: ./suggested.md#building-with-system-llvm
+[sysllvm]: ./suggested.md#skipping-llvm-build
 
 ## Creating a target specification
 

src/building/prerequisites.md

@@ -19,7 +19,7 @@ If building LLVM from source (the default), you'll need additional tools:
 Otherwise, you'll need LLVM installed and `llvm-config` in your path.
 See [this section for more info][sysllvm].
 
-[sysllvm]: ./suggested.md#building-with-system-llvm
+[sysllvm]: ./suggested.md#skipping-llvm-build
 
 ### Windows