Refactor isThumb1Only() && isMClass() into a predicate called isV6M()

This must be enforced for all v6M cores, not just the cortex-m0,
irregardless of the user-specified alignment.

Patch by Charlie Turner.

llvm-svn: 219300
diff --git a/llvm/lib/Target/ARM/ARMSubtarget.h b/llvm/lib/Target/ARM/ARMSubtarget.h
index c6e756c..8c85ad7 100644
--- a/llvm/lib/Target/ARM/ARMSubtarget.h
+++ b/llvm/lib/Target/ARM/ARMSubtarget.h
@@ -405,6 +405,10 @@
   bool isRClass() const { return ARMProcClass == RClass; }
   bool isAClass() const { return ARMProcClass == AClass; }
 
+  bool isV6M() const {
+    return isThumb1Only() && isMClass();
+  }
+
   bool isR9Reserved() const { return IsR9Reserved; }
 
   bool useMovt(const MachineFunction &MF) const;