Revert rGf0bab7875e78e01c149d12302dcc4b6d4c43e25c - "Triple.h - reduce Twine.h include to forward declarations. NFC."

This causes ICEs on the clang-ppc64be buildbots and I've limited ability to triage the problem.

include/llvm/ADT/Triple.h

@@ -9,8 +9,7 @@
 #ifndef LLVM_ADT_TRIPLE_H
 #define LLVM_ADT_TRIPLE_H
 
-#include "llvm/ADT/StringRef.h"
-#include <cassert>
+#include "llvm/ADT/Twine.h"
 
 // Some system headers or GCC predefined macros conflict with identifiers in
 // this file.  Undefine them here.
@@ -20,7 +19,6 @@
 
 namespace llvm {
 
-class Twine;
 class VersionTuple;
 
 /// Triple - Helper class for working with autoconf configuration names. For

include/llvm/Support/TargetRegistry.h

@@ -22,7 +22,6 @@
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
-#include "llvm/ADT/Twine.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/CodeGen.h"
 #include "llvm/Support/ErrorHandling.h"

lib/MC/MCSectionELF.cpp

@@ -8,7 +8,6 @@
 
 #include "llvm/MC/MCSectionELF.h"
 #include "llvm/ADT/Triple.h"
-#include "llvm/ADT/Twine.h"
 #include "llvm/BinaryFormat/ELF.h"
 #include "llvm/MC/MCAsmInfo.h"
 #include "llvm/MC/MCExpr.h"

lib/Support/Triple.cpp

@@ -11,7 +11,6 @@
 #include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
-#include "llvm/ADT/Twine.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/SwapByteOrder.h"
@@ -19,7 +18,6 @@
 #include "llvm/Support/VersionTuple.h"
 #include <cassert>
 #include <cstring>
-
 using namespace llvm;
 
 StringRef Triple::getArchTypeName(ArchType Kind) {

unittests/ADT/TripleTest.cpp

@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ADT/Triple.h"
-#include "llvm/ADT/Twine.h"
 #include "llvm/Support/VersionTuple.h"
 #include "gtest/gtest.h"
 

unittests/Frontend/OpenMPContextTest.cpp

@@ -8,7 +8,6 @@
 
 #include "llvm/Frontend/OpenMP/OMPConstants.h"
 #include "llvm/Frontend/OpenMP/OMPContext.h"
-#include "llvm/ADT/Twine.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;

unittests/Support/ThreadPool.cpp

@@ -12,7 +12,6 @@
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Triple.h"
-#include "llvm/ADT/Twine.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/Threading.h"