Don't use std::errc.

As noted on Errc.h:

// * std::errc is just marked with is_error_condition_enum. This means that
//   common patters like AnErrorCode == errc::no_such_file_or_directory take
//   4 virtual calls instead of two comparisons.

And on some libstdc++ those virtual functions conclude that

------------------------
int main() {
  std::error_code foo = std::make_error_code(std::errc::no_such_file_or_directory);
  return foo == std::errc::no_such_file_or_directory;
}
-------------------------

should exit with 0.

llvm-svn: 239683
diff --git a/llvm/lib/Object/ArchiveWriter.cpp b/llvm/lib/Object/ArchiveWriter.cpp
index 90a736f..dcd6ad7 100644
--- a/llvm/lib/Object/ArchiveWriter.cpp
+++ b/llvm/lib/Object/ArchiveWriter.cpp
@@ -18,6 +18,7 @@
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Object/SymbolicFile.h"
+#include "llvm/Support/Errc.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/Path.h"
@@ -70,7 +71,7 @@
   // Linux cannot open directories with open(2), although
   // cygwin and *bsd can.
   if (NewStatus.type() == sys::fs::file_type::directory_file)
-    return make_error_code(std::errc::is_a_directory);
+    return make_error_code(errc::is_a_directory);
 
   return NewFD;
 }