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>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231987 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/PowerPC/PPCTargetMachine.cpp

@@ -160,11 +160,11 @@ PPCTargetMachine::PPCTargetMachine(const Target &T, StringRef TT, StringRef CPU,
                                    StringRef FS, const TargetOptions &Options,
                                    Reloc::Model RM, CodeModel::Model CM,
                                    CodeGenOpt::Level OL)
-    : LLVMTargetMachine(T, TT, CPU, computeFSAdditions(FS, OL, TT), Options, RM,
-                        CM, OL),
+    : LLVMTargetMachine(T, getDataLayoutString(Triple(TT)), TT, CPU,
+                        computeFSAdditions(FS, OL, TT), Options, RM, CM, OL),
       TLOF(createTLOF(Triple(getTargetTriple()))),
       TargetABI(computeTargetABI(Triple(TT), Options)),
-      DL(getDataLayoutString(Triple(TT))), Subtarget(TT, CPU, TargetFS, *this) {
+      Subtarget(TT, CPU, TargetFS, *this) {
   initAsmInfo();
 }