Simplify std::scoped_lock destructor

	* include/std/mutex (scoped_lock::~scoped_lock()): Use fold
	expression.

From-SVN: r272187

libstdc++-v3/ChangeLog

 2019-06-12  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/mutex (scoped_lock::~scoped_lock()): Use fold
+	expression.
+
 	* include/Makefile.am: Add new <bits/charconv.h> header.
 	* include/Makefile.in: Regenerate.
 	* include/bits/basic_string.h (to_string(int), to_string(unsigned))

libstdc++-v3/include/std/mutex

@@ -576,11 +576,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       { } // calling thread owns mutex
 
       ~scoped_lock()
-      {
-	std::apply([](_MutexTypes&... __m) {
-	  char __i[] __attribute__((__unused__)) = { (__m.unlock(), 0)... };
-	}, _M_devices);
-      }
+      { std::apply([](auto&... __m) { (__m.unlock(), ...); }, _M_devices); }
 
       scoped_lock(const scoped_lock&) = delete;
       scoped_lock& operator=(const scoped_lock&) = delete;