[mlir] Initialize DefaultTimingManager::out. (#87522)

`DefaultTimingManager::clear()` uses `out` to initialize `TimerImpl`,
but the `out` is `nullptr` by default. This means if
`DefaultTimingManager::setOutput()` is never called,
`DefaultTimingManager` destructor may generate SIGSEGV.

Author: wecing

mlir/lib/Support/Timing.cpp

@@ -499,7 +499,8 @@ class DefaultTimingManagerImpl {
 } // namespace mlir
 
 DefaultTimingManager::DefaultTimingManager()
-    : impl(std::make_unique<DefaultTimingManagerImpl>()) {
+    : impl(std::make_unique<DefaultTimingManagerImpl>()),
+      out(std::make_unique<OutputTextStrategy>(llvm::errs())) {
   clear(); // initializes the root timer
 }