UnRevert "Revert the archive part of "Support/PathV2: Add identify_magic.""

This reverts commit dd103021a889a986a181ce36ed7b0e8dc9b645e1.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123595 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Archive/Archive.cpp b/lib/Archive/Archive.cpp
index 3ee3cb2..1eab27d 100644
--- a/lib/Archive/Archive.cpp
+++ b/lib/Archive/Archive.cpp
@@ -116,11 +116,10 @@
 
   // Get the signature and status info
   const char* signature = (const char*) data;
-  std::string magic;
+  SmallString<4> magic;
   if (!signature) {
-    path.getMagicNumber(magic,4);
+    sys::fs::get_magic(path.str(), magic.capacity(), magic);
     signature = magic.c_str();
-    std::string err;
     const sys::FileStatus *FSinfo = path.getFileStatus(false, ErrMsg);
     if (FSinfo)
       info = *FSinfo;