Share SetupCRT with the unit tests so they can't pop a modal dialog

UnitTest.exe runs on CI and from tooling, where an assert or an abort() puts
up a message box that nothing will ever click, and the run just hangs until it
is killed. Headless already solved this; move its SetupCRT() into Common
(ExceptionHandlerSetup, which is where the rest of the process-level fault
setup lives) and call it from the unit tests too.

No behaviour change for headless. The OS-level SetErrorMode() call is now
guarded for UWP, which doesn't have it.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01GZq8ZtJmFY7bkX5FVkr3P9

Common/ExceptionHandlerSetup.cpp

@@ -20,9 +20,42 @@
 #include "Common/MachineContext.h"
 #include "Common/ExceptionHandlerSetup.h"
 
+#if defined(_MSC_VER)
+#include <crtdbg.h>
+#include "Common/CommonWindows.h"
+#endif
+
 static BadAccessHandler g_badAccessHandler;
 static void *altStack = nullptr;
 
+void SetupCRT(bool suppressDialogs) {
+#if defined(_MSC_VER)
+	_CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
+
+	if (suppressDialogs) {
+		// 1. Redirect CRT assertions/errors/warnings to stderr.
+		const _HFILE reportTarget = _CRTDBG_FILE_STDERR;
+
+		_CrtSetReportMode(_CRT_ASSERT, _CRTDBG_MODE_FILE);
+		_CrtSetReportFile(_CRT_ASSERT, reportTarget);
+
+		_CrtSetReportMode(_CRT_ERROR, _CRTDBG_MODE_FILE);
+		_CrtSetReportFile(_CRT_ERROR, reportTarget);
+
+		_CrtSetReportMode(_CRT_WARN, _CRTDBG_MODE_FILE);
+		_CrtSetReportFile(_CRT_WARN, reportTarget);
+
+		// 2. Suppress the abort() message box & crash reporting dialogs.
+		_set_abort_behavior(0, _WRITE_ABORT_MSG | _CALL_REPORTFAULT);
+
+#if !PPSSPP_PLATFORM(UWP)
+		// 3. Suppress Windows OS-level "Program has stopped working" modal dialogs.
+		SetErrorMode(SEM_FAILCRITICALERRORS | SEM_NOGPFAULTERRORBOX);
+#endif
+	}
+#endif
+}
+
 #ifdef MACHINE_CONTEXT_SUPPORTED
 
 // We cannot handle exceptions in UWP builds. Bleh.