[lld] unified COFF and ELF error handling on new Common/ErrorHandler

Summary:
The COFF linker and the ELF linker have long had similar but separate
Error.h and Error.cpp files to implement error handling. This change
introduces new error handling code in Common/ErrorHandler.h, changes the
COFF and ELF linkers to use it, and removes the old, separate
implementations.

Reviewers: ruiu

Reviewed By: ruiu

Subscribers: smeenai, jyknight, emaste, sdardis, nemanjai, nhaehnle, mgorny, javed.absar, kbarton, fedor.sergeev, llvm-commits

Differential Revision: https://reviews.llvm.org/D39259

llvm-svn: 316624
diff --git a/lld/ELF/Symbols.cpp b/lld/ELF/Symbols.cpp
index 354d2cc..8f6b408 100644
--- a/lld/ELF/Symbols.cpp
+++ b/lld/ELF/Symbols.cpp
@@ -8,7 +8,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "Symbols.h"
-#include "Error.h"
 #include "InputFiles.h"
 #include "InputSection.h"
 #include "OutputSections.h"
@@ -17,6 +16,7 @@
 #include "Target.h"
 #include "Writer.h"
 
+#include "lld/Common/ErrorHandler.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Path.h"
 #include <cstring>