[libclc] Fix link to source in index.html (llvm#167494)

Author: kwk

libclc/www/index.html

@@ -43,7 +43,7 @@ <h1>libclc</h1>
 
 <h2>Download</h2>
 
-<tt>git clone https://github.com/llvm/llvm-project.git</tt> (<a href="https://github.com/llvm/llvm-project/tree/libclc">View sources</a>)
+<tt>git clone https://github.com/llvm/llvm-project.git</tt> (<a href="https://github.com/llvm/llvm-project/tree/main/libclc">View sources</a>)
 
 <h2>Discourse forums</h2>