[compiler-rt][docs] Update license info

[zbrid]

Summary

Remove reference to the old LLVM license and replace with a ref to
the new LLVM license. My understanding is that everything is under
the Apache License now, so I updated the compiler-rt homepage to
say the same thing llvm.org says.

[echristo]

Adding Petr here since he looked at this most recently.

[phosek]

I'm not sure about the "All of the" part; LLVM front page says just "Code in the LLVM project is licensed under the Apache 2.0 License with LLVM exceptions". While the code in compiler-rt project is licensed under Apache 2.0 license with LLVM exceptions, not all of the existing code has been relicensed under the new license. I'd recommend checking this with the LLVM foundation, I've also added @chandlerc who might be able to help.

compiler-rt/www/index.html

<div id="content">
   <li>
     <b>BlocksRuntime</b> - a target-independent implementation of Apple "Blocks"
     runtime interfaces.
   </li>
   </ul>
   </p>
 
   <p>All of the code in the compiler-rt project is <a
-     href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">dual licensed</a>
-     under the MIT license and the UIUC License (a BSD-like license).</p>
+     href="https://llvm.org/docs/DeveloperPolicy.html#copyright-license-and-patents">licensed</a>
+     under the Apache 2.0 License with LLVM exceptions.</p>
 
   <!--=====================================================================-->
   <h2 id="users">Clients</h2>
   <!--=====================================================================-->
 
   <p>Currently compiler-rt is primarily used by
     the <a href="https://clang.llvm.org">Clang</a>
     and <a href="https://llvm.org">LLVM</a> projects as the implementation for