lld-link: Add some entries to the 8.0 release notes

[ruiu]

LGTM

lld/branches/release_80/docs/ReleaseNotes.rst

* lld now uses the ``sigrie`` instruction as a trap instruction for
   MIPS targets.
 
 COFF Improvements
 -----------------
 
 * PDB GUID is set to hash of PDB contents instead to a random byte
   sequence for build reproducibility.
 
+* ``/pdbsourcepath:`` is now also used to make ``"cwd"``, ``"exe"``, ``"pdb"``
+  in the env block of PDB outputs absolute if they are relative, and to make
+  paths to obj files referenced in PDB outputs absolute if they are relative.
+  Together with the previous item, this makes it possible to generate
+  executables and PDBs that are fully deterministic and independent of the
+  absolute path to the build directory, so that different machines building
+  the same code in different directories can produce exactly the same output.
+
 * The following flags have been added: ``/force:multiple``
 
 * lld now can link against import libraries produced by GNU tools.
 
 * lld can create thunks for ARM, to allow linking images over 16 MB.
 
+* Several speed and memory usage improvements.
+
+* lld now creates debug info for typedefs.
+
+* lld can now link obj files produced by ``cl.exe /Z7 /Yc``.
+
+* lld now understands ``%_PDB%`` and ``%_EXT%`` in ``/pdbaltpath:``.
+
+* Undefined symbols are now printed in demangled form in addition to raw form.
+
 MinGW Improvements
 ------------------
 
 * lld can now automatically import data variables from DLLs without the
   use of the dllimport attribute.
 
 * lld can now use existing normal MinGW sysroots with import libraries and
   CRT startup object files for GNU binutils. lld can handle most object