[PrintAsObjC] Sentence-case the enum case name when appending it to the enum name.

Otherwise, we cram a conventionally UpperCamelCase thing with a
newly-conventinally-lowerCamelCased thing together and destroy the
word boundaries. Fixes rdar://problem/24947695.

Author: DougGregor

lib/PrintAsObjC/PrintAsObjC.cpp

@@ -18,6 +18,7 @@
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/TypeVisitor.h"
 #include "swift/AST/Comment.h"
+#include "swift/Basic/StringExtras.h"
 #include "swift/Basic/Version.h"
 #include "swift/ClangImporter/ClangImporter.h"
 #include "swift/Frontend/Frontend.h"
@@ -264,7 +265,9 @@ class ObjCPrinter : private DeclVisitor<ObjCPrinter>,
         } else {
           os << customName;
         }
-        os << Elt->getName();
+
+        SmallString<16> scratch;
+        os << camel_case::toSentencecase(Elt->getName().str(), scratch);
       } else {
         os << customEltName
            << " SWIFT_COMPILE_NAME(\"" << Elt->getName() << "\")";

test/PrintAsObjC/enums.swift

@@ -36,10 +36,12 @@ import Foundation
 // CHECK-NEXT:   ObjcEnumNamedA = 0,
 // CHECK-NEXT:   ObjcEnumNamedB = 1,
 // CHECK-NEXT:   ObjcEnumNamedC = 2,
+// CHECK-NEXT:   ObjcEnumNamedD = 3,
+// CHECK-NEXT:   ObjcEnumNamedHelloDolly = 4,
 // CHECK-NEXT: };
 
 @objc(ObjcEnumNamed) enum EnumNamed: Int {
-  case A, B, C
+  case A, B, C, d, helloDolly
 }
 
 // CHECK-LABEL: typedef SWIFT_ENUM(NSInteger, EnumWithNamedConstants) {