MC: Remove MCSubtargetInfo() default constructor

Force all creators of `MCSubtargetInfo` to immediately initialize it,
merging the default constructor and the initializer into an initializing
constructor.  Besides cleaning up the code a little, this makes it clear
that the initializer is never called again later.

Out-of-tree backends need a trivial change: instead of calling:

    auto *X = new MCSubtargetInfo();
    InitXYZMCSubtargetInfo(X, ...);
    return X;

they should call:

    return createXYZMCSubtargetInfoImpl(...);

There's no real functionality change here.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@241957 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/TargetSubtargetInfo.cpp

@@ -19,7 +19,14 @@ using namespace llvm;
 //---------------------------------------------------------------------------
 // TargetSubtargetInfo Class
 //
-TargetSubtargetInfo::TargetSubtargetInfo() {}
+TargetSubtargetInfo::TargetSubtargetInfo(
+    const Triple &TT, StringRef CPU, StringRef FS,
+    ArrayRef<SubtargetFeatureKV> PF, ArrayRef<SubtargetFeatureKV> PD,
+    const SubtargetInfoKV *ProcSched, const MCWriteProcResEntry *WPR,
+    const MCWriteLatencyEntry *WL, const MCReadAdvanceEntry *RA,
+    const InstrStage *IS, const unsigned *OC, const unsigned *FP)
+    : MCSubtargetInfo(TT, CPU, FS, PF, PD, ProcSched, WPR, WL, RA, IS, OC, FP) {
+}
 
 TargetSubtargetInfo::~TargetSubtargetInfo() {}