Rename two clang tests from .cc to .cpp.

clang/test/lit.cfg.py doesn't list .cc as test extension, so these
tests never ran.

Tweak one of the two tests to actually pass, now that it runs.
(The other one was already passing.)

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@367574 91177308-0d34-0410-b5e6-96231b3b80d8

test/Analysis/structured_bindings.cc → test/Analysis/structured_bindings.cpp

@@ -1,10 +1,9 @@
 // RUN: %clang_analyze_cc1 -std=c++17 -analyzer-checker=core -verify %s
 
-// expected-no-diagnostics
 struct s { int a; };
 int foo() {
     auto[a] = s{1}; // FIXME: proper modelling
     if (a) {
     }
-}
+} // expected-warning{{control reaches end of non-void function}}