Move the DataLayout to the generic TargetMachine, making it mandatory.

Summary:
I don't know why every singled backend had to redeclare its own DataLayout.
There was a virtual getDataLayout() on the common base TargetMachine, the
default implementation returned nullptr. It was not clear from this that
we could assume at call site that a DataLayout will be available with
each Target.

Now getDataLayout() is no longer virtual and return a pointer to the
DataLayout member of the common base TargetMachine. I plan to turn it into
a reference in a future patch.

The only backend that didn't have a DataLayout previsouly was the CPPBackend.
It now initializes the default DataLayout. This commit is NFC for all the
other backends.

Test Plan: clang+llvm ninja check-all

Reviewers: echristo

Subscribers: jfb, jholewinski, llvm-commits

Differential Revision: http://reviews.llvm.org/D8243

From: Mehdi Amini <mehdi.amini@apple.com>
llvm-svn: 231987
diff --git a/llvm/lib/Target/CppBackend/CPPTargetMachine.h b/llvm/lib/Target/CppBackend/CPPTargetMachine.h
index 4bae7f8..96d832d 100644
--- a/llvm/lib/Target/CppBackend/CPPTargetMachine.h
+++ b/llvm/lib/Target/CppBackend/CPPTargetMachine.h
@@ -26,11 +26,11 @@
 };
 
 struct CPPTargetMachine : public TargetMachine {
-  CPPTargetMachine(const Target &T, StringRef TT,
-                   StringRef CPU, StringRef FS, const TargetOptions &Options,
-                   Reloc::Model RM, CodeModel::Model CM,
-                   CodeGenOpt::Level OL)
-    : TargetMachine(T, TT, CPU, FS, Options), Subtarget() {}
+  CPPTargetMachine(const Target &T, StringRef TT, StringRef CPU, StringRef FS,
+                   const TargetOptions &Options, Reloc::Model RM,
+                   CodeModel::Model CM, CodeGenOpt::Level OL)
+      : TargetMachine(T, "", TT, CPU, FS, Options), Subtarget() {}
+
 private:
   CPPSubtarget Subtarget;