[LanguageRuntime] Introduce LLVM-style casts

Summary:
Using llvm-style rtti gives us stronger guarantees around casting
LanguageRuntimes.

As discussed in D62755

Differential Revision: https://reviews.llvm.org/D62934

llvm-svn: 362884
diff --git a/lldb/source/Plugins/Language/ObjC/CF.cpp b/lldb/source/Plugins/Language/ObjC/CF.cpp
index 7db55e1..e1816a2 100644
--- a/lldb/source/Plugins/Language/ObjC/CF.cpp
+++ b/lldb/source/Plugins/Language/ObjC/CF.cpp
@@ -50,9 +50,7 @@
   if (!process_sp)
     return false;
 
-  ObjCLanguageRuntime *runtime =
-      (ObjCLanguageRuntime *)process_sp->GetLanguageRuntime(
-          lldb::eLanguageTypeObjC);
+  ObjCLanguageRuntime *runtime = process_sp->GetObjCLanguageRuntime();
 
   if (!runtime)
     return false;
@@ -114,9 +112,7 @@
   if (!process_sp)
     return false;
 
-  ObjCLanguageRuntime *runtime =
-      (ObjCLanguageRuntime *)process_sp->GetLanguageRuntime(
-          lldb::eLanguageTypeObjC);
+  ObjCLanguageRuntime *runtime = process_sp->GetObjCLanguageRuntime();
 
   if (!runtime)
     return false;
@@ -236,9 +232,7 @@
   if (!process_sp)
     return false;
 
-  ObjCLanguageRuntime *runtime =
-      (ObjCLanguageRuntime *)process_sp->GetLanguageRuntime(
-          lldb::eLanguageTypeObjC);
+  ObjCLanguageRuntime *runtime = process_sp->GetObjCLanguageRuntime();
 
   if (!runtime)
     return false;