Add note on libFuzzer for Windows to release notes

[metzman]

• be more specific

[metzman]

Please take a look @hans
Please let me know if I'm mistakenly adding this to master.
Thanks!

cc @kcc

[hans]

lgtm

I don't think committing to the branch works from the monorepo, so either check out the branch with svn (svn co https://llvm.org/svn/llvm-project/llvm/branches/release_80/docs/), or let me know and I'll commit for you.

[metzman]

In D58676#1410659, @hans wrote:

lgtm

I don't think committing to the branch works from the monorepo, so either check out the branch with svn (svn co https://llvm.org/svn/llvm-project/llvm/branches/release_80/docs/), or let me know and I'll commit for you.

Could you merge it for me please? I'm using the git monorepo and I haven't really used svn before.
Thanks!

llvm/branches/release_80/docs/ReleaseNotes.rst

* Support for profile-driven software cache prefetching on X86. This is part of
   performed at a specified fixed offset from such an instruction's memory
   operand. Next, this information needs to be converted to the AutoFDO syntax
   and the resulting profile may be passed back to the compiler with the LLVM
   flag ``-prefetch-hints-file``, together with the exact same set of
   compilation parameters used for the original binary. More information is
   available in the `RFC
   <https://lists.llvm.org/pipermail/llvm-dev/2018-November/127461.html>`_.
 
+* Windows support for libFuzzer (x86_64).
+
 .. NOTE
    If you would like to document a larger change, then you can add a
    subsection about it right here. You can copy the following boilerplate
    and un-indent it (the indentation causes it to be inside this comment).
 
    Special New Feature
    -------------------