Cast void pointer before deallocating with delete[]

The stack memory is a `void*` which creates a warning when using
the `delete[]` operator because it is unable to call the destructor of
of an unknown object type.

Author: hugueskamba

rtos/source/Thread.cpp

@@ -113,7 +113,8 @@ osStatus Thread::start(mbed::Callback<void()> task)
     _tid = osThreadNew(Thread::_thunk, this, &_attr);
     if (_tid == nullptr) {
         if (_dynamic_stack) {
-            delete[] _attr.stack_mem;
+            // Cast before deallocation as delete[] does not accept void*
+            delete[] static_cast<uint32_t *>(_attr.stack_mem);
             _attr.stack_mem = nullptr;
         }
         _mutex.unlock();
@@ -417,7 +418,8 @@ Thread::~Thread()
     // terminate is thread safe
     terminate();
     if (_dynamic_stack) {
-        delete[] _attr.stack_mem;
+        // Cast before deallocation as delete[] does not accept void*
+        delete[] static_cast<uint32_t *>(_attr.stack_mem);
         _attr.stack_mem = nullptr;
     }
 }