Support Swift calling convention for PPC64 targets

This adds basic support for the Swift calling convention with PPC64 targets.
Patch provided by Atul Sowani in bug report #37223

llvm-svn: 333316
diff --git a/clang/lib/Basic/Targets/PPC.h b/clang/lib/Basic/Targets/PPC.h
index 629e4cf..9ea100f 100644
--- a/clang/lib/Basic/Targets/PPC.h
+++ b/clang/lib/Basic/Targets/PPC.h
@@ -335,6 +335,15 @@
     }
     return false;
   }
+
+  CallingConvCheckResult checkCallingConvention(CallingConv CC) const override {
+    switch (CC) {
+    case CC_Swift:
+      return CCCR_OK;
+    default:
+      return CCCR_Warning;
+    }
+  }
 };
 
 class LLVM_LIBRARY_VISIBILITY DarwinPPC32TargetInfo