Ignore "no-frame-pointer-elim" and "no-frame-pointer-elim-non-leaf" in favor of "frame-pointer"

D56351 (included in LLVM 8.0.0) introduced "frame-pointer".  All tests
which use "no-frame-pointer-elim" or "no-frame-pointer-elim-non-leaf"
have been migrated to use "frame-pointer".

Implement UpgradeFramePointerAttributes to upgrade the two obsoleted
function attributes for bitcode. Their semantics are ignored.

Differential Revision: https://reviews.llvm.org/D71863
diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst
index 1b25a3f..96331a7 100644
--- a/llvm/docs/ReleaseNotes.rst
+++ b/llvm/docs/ReleaseNotes.rst
@@ -93,6 +93,11 @@
 * ``Callbacks`` have been added to ``CommandLine Options``.  These can
   be used to validate of selectively enable other options.
 
+* The function attributes ``no-frame-pointer-elim`` and
+  ``no-frame-pointer-elim-non-leaf`` have been replaced by ``frame-pointer``,
+  which has 3 values: ``none``, ``non-leaf``, and ``all``. The values mean what
+  functions should retain frame pointers.
+
 Changes to the LLVM IR
 ----------------------