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/ArchiveWriter.cpp b/lib/Archive/ArchiveWriter.cpp
index 07a9aaf..8fcc7aa 100644
--- a/lib/Archive/ArchiveWriter.cpp
+++ b/lib/Archive/ArchiveWriter.cpp
@@ -181,9 +181,11 @@
     flags |= ArchiveMember::HasPathFlag;
   if (hasSlash || filePath.str().length() > 15)
     flags |= ArchiveMember::HasLongFilenameFlag;
-  std::string magic;
-  mbr->path.getMagicNumber(magic,4);
-  switch (sys::IdentifyFileType(magic.c_str(),4)) {
+
+  sys::LLVMFileType type;
+  if (sys::fs::identify_magic(mbr->path.str(), type))
+    type = sys::Unknown_FileType;
+  switch (type) {
     case sys::Bitcode_FileType:
       flags |= ArchiveMember::BitcodeFlag;
       break;