[clang] Permit lifetimebound in all language modes (llvm#115482)

Lifetimebound annotations can help diagnose common cases of dangling
including escaping the address of a stack variable from a function. This
is useful in all C family languages, restricting these diagnostics to
C++ is an artificial limitation.

Co-authored-by: Gabor Horvath <[email protected]>

Author: Xazax-hun

clang/include/clang/Basic/Attr.td

@@ -1837,7 +1837,6 @@ def LifetimeBound : DeclOrTypeAttr {
   let Spellings = [Clang<"lifetimebound", 0>];
   let Subjects = SubjectList<[ParmVar, ImplicitObjectParameter], ErrorDiag>;
   let Documentation = [LifetimeBoundDocs];
-  let LangOpts = [CPlusPlus];
   let SimpleHandler = 1;
 }
 

clang/test/Sema/attr-lifetimebound.c

@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -std=c99 -verify %s
+
+int *f(int* p __attribute__((lifetimebound)));
+
+int *g() {
+  int i;
+  return f(&i); // expected-warning {{address of stack memory associated with local variable 'i' returned}}
+}