[lld] Remove unnecessary llvm/Config/config.h includes

[mgorny]

Summary

Remove the includes of <llvm/Config/config.h> private LLVM header.
The relevant files seem not to use any definitions from that file,
and it is not available when building against installed LLVM.

The use in lib/ReaderWriter/MachO/MachOLinkingContext.cpp originates
from rL218718, and the use in ELF/Strings.cpp from rL274804 (where it
was moved from Symbols.cpp). In both cases, they were added as a part of
demangling support, and they provided HAVE_CXXABI_H.

Since we are now using the LLVM demangler library instead, the code was
removed and the includes and no longer necessary.

[ruiu]

LGTM. Thanks you for doing this!

[mgorny]

Thanks for the quick review ;-).

ELF/Strings.cpp

 //===- Strings.cpp -------------------------------------------------------===//
 //
 //                             The LLVM Linker
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "Strings.h"
 #include "Config.h"
 #include "Error.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Twine.h"
-#include "llvm/Config/config.h"
 #include "llvm/Demangle/Demangle.h"
 #include <algorithm>
 #include <cstring>
 
 using namespace llvm;
 using namespace lld;
 using namespace lld::elf;
 

lib/ReaderWriter/MachO/MachOLinkingContext.cpp

 #include "lld/Core/ArchiveLibraryFile.h"
 #include "lld/Core/PassManager.h"
 #include "lld/Core/Reader.h"
 #include "lld/Core/Writer.h"
 #include "lld/Driver/Driver.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/Triple.h"
-#include "llvm/Config/config.h"
 #include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/MachO.h"
 #include "llvm/Support/Path.h"
 #include <algorithm>