[Frontend] Treat function with skipped body as definition

[ilya-biryukov]

Summary

This fixes an invalid warning about missing definition of a function when
parsing with SkipFunctionBodies=true

[ilya-biryukov]

• Reverted accidental whitespace change.

[sepavloff]

LGTM.

Thanks!

include/clang/AST/Decl.h

public:
   }
 
   /// Returns whether this specific declaration of the function is also a
   /// definition that does not contain uninstantiated body.
   ///
   /// This does not determine whether the function has been defined (e.g., in a
   /// previous definition); for that information, use isDefined.
   bool isThisDeclarationADefinition() const {
-    return IsDeleted || IsDefaulted || Body || IsLateTemplateParsed ||
-      WillHaveBody || hasDefiningAttr();
+    return IsDeleted || IsDefaulted || Body || HasSkippedBody ||
+           IsLateTemplateParsed || WillHaveBody || hasDefiningAttr();
   }
 
   /// doesThisDeclarationHaveABody - Returns whether this specific
   /// declaration of the function has a body - that is, if it is a non-
   /// deleted definition.
   bool doesThisDeclarationHaveABody() const {
     return Body || IsLateTemplateParsed;
   }

test/Index/skipped_function_bodies.cpp

+// RUN: env CINDEXTEST_SKIP_FUNCTION_BODIES=1 c-index-test -test-load-source all %s 2>&1 \
+// RUN: | FileCheck %s
+
+inline int with_body() { return 10; }
+inline int without_body();
+
+int x = with_body() + without_body();
+// CHECK: warning: inline function 'without_body' is not defined
+// CHECK-NOT: warning: inline function 'with_body' is not defined