[XCOFF] Add functionality for parsing AIX XCOFF object file headers

Summary:
1. Add functionality for parsing AIX XCOFF object files headers.
2. Only support 32-bit AIX XCOFF object files in this patch.
3. Print out the AIX XCOFF object file header in YAML format.

Reviewers: sfertile, hubert.reinterpretcast, jasonliu, mstorsjo, zturner, rnk

Reviewed By: sfertile, hubert.reinterpretcast

Subscribers: jsji, mgorny, hiraditya, jdoerfert, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59419

Patch by Digger Lin


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357663 91177308-0d34-0410-b5e6-96231b3b80d8

lib/BinaryFormat/Magic.cpp

@@ -61,6 +61,13 @@ file_magic llvm::identify_magic(StringRef Magic) {
       return file_magic::wasm_object;
     break;
   }
+
+  case 0x01:
+    // XCOFF format
+    if (startswith(Magic, "\x01\xDF"))
+      return file_magic::xcoff_object_32;
+    break;
+
   case 0xDE: // 0x0B17C0DE = BC wraper
     if (startswith(Magic, "\xDE\xC0\x17\x0B"))
       return file_magic::bitcode;