Enable control flow checks for functions without body

Except checks for tail recursive calls

 #KT-7796 Fixed

compiler/frontend/src/org/jetbrains/kotlin/cfg/ControlFlowInformationProvider.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2016 JetBrains s.r.o.
+ * Copyright 2010-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -879,6 +879,7 @@ class ControlFlowInformationProvider private constructor(
 
     private fun markAndCheckRecursiveTailCalls(subroutineDescriptor: FunctionDescriptor) {
         if (!subroutineDescriptor.isTailrec) return
+        if (subroutine is KtNamedFunction && !subroutine.hasBody()) return
 
         // finally blocks are copied which leads to multiple diagnostics reported on one instruction
         class KindAndCall(var kind: TailRecursionKind, internal val call: ResolvedCall<*>)

compiler/frontend/src/org/jetbrains/kotlin/resolve/ControlFlowAnalyzer.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2017 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -103,7 +103,6 @@ public class ControlFlowAnalyzer {
     }
 
     private void checkFunction(@NotNull BodiesResolveContext c, @NotNull KtDeclarationWithBody function, @Nullable KotlinType expectedReturnType) {
-        if (!function.hasBody()) return;
         ControlFlowInformationProvider controlFlowInformationProvider =
                 new ControlFlowInformationProvider(function, trace, languageVersionSettings);
         if (c.getTopDownAnalysisMode().isLocalDeclarations()) {