[BinaryFormat] Identify AArch64 COFF files

Differential Revision: https://reviews.llvm.org/D34742

llvm-svn: 306647
diff --git a/llvm/lib/BinaryFormat/Magic.cpp b/llvm/lib/BinaryFormat/Magic.cpp
index ca4d93f..5d0a71f 100644
--- a/llvm/lib/BinaryFormat/Magic.cpp
+++ b/llvm/lib/BinaryFormat/Magic.cpp
@@ -190,8 +190,8 @@
     }
     break;
 
-  case 0x64: // x86-64 Windows.
-    if (Magic[1] == char(0x86))
+  case 0x64: // x86-64 or ARM64 Windows.
+    if (Magic[1] == char(0x86) || Magic[1] == char(0xaa))
       return file_magic::coff_object;
     break;