[COFF, ARM64] Implement llvm.addressofreturnaddress intrinsic

Reviewers: rnk, mstorsjo, efriedma, TomTan

Reviewed By: efriedma

Subscribers: javed.absar, kristof.beyls, chrib, llvm-commits

Differential Revision: https://reviews.llvm.org/D53962

llvm-svn: 345892
diff --git a/llvm/docs/LangRef.rst b/llvm/docs/LangRef.rst
index 39134fa..8ec5178 100644
--- a/llvm/docs/LangRef.rst
+++ b/llvm/docs/LangRef.rst
@@ -10328,7 +10328,7 @@
 other aggressive transformations, so the value returned may not be that
 of the obvious source-language caller.
 
-This intrinsic is only implemented for x86.
+This intrinsic is only implemented for x86 and aarch64.
 
 '``llvm.frameaddress``' Intrinsic
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^