Move endian constant from Host.h to SwapByteOrder.h, prune include

Works on this dependency chain:
  ArrayRef.h ->
  Hashing.h -> --CUT--
  Host.h ->
  StringMap.h / StringRef.h

ArrayRef is very popular, but Host.h is rarely needed. Move the
IsBigEndianHost constant to SwapByteOrder.h. Clients of that header are
more likely to need it.

git-svn-id: https://llvm.org/svn/llvm-project/lld/trunk@375316 91177308-0d34-0410-b5e6-96231b3b80d8

include/lld/Common/LLVM.h

@@ -17,6 +17,7 @@
 // This should be the only #include, force #includes of all the others on
 // clients.
 #include "llvm/ADT/Hashing.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Casting.h"
 #include <utility>
 

include/lld/Core/File.h

@@ -16,6 +16,7 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Twine.h"
+#include "llvm/Support/Allocator.h"
 #include "llvm/Support/ErrorHandling.h"
 #include <functional>
 #include <memory>

lib/ReaderWriter/MachO/DebugInfo.h

@@ -12,6 +12,7 @@
 #include "lld/Core/Atom.h"
 #include <vector>
 
+#include "llvm/Support/Allocator.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/raw_ostream.h"
 

tools/lld/lld.cpp

@@ -33,6 +33,7 @@
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Host.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/Path.h"
 #include <cstdlib>