crt: test: Replace usage of _beginthreadex() by CreateThread() in t_safe_flush.c test

t_safe_flush.c is spawning new thread via _beginthreadex() which only uses
WinAPI functions. So it does not need to use CRT function _beginthreadex()
for spawning thread and WinAPI CreateThread() is enough.

crtdll.dll does not contain _beginthreadex(), so this change allows to
compile t_safe_flush.c test against crtdll.dll.

Signed-off-by: LIU Hao <lh_mouse@126.com>

mingw-w64-crt/testcases/t_safe_flush.c

diff --git a/mingw-w64-crt/testcases/t_safe_flush.c b/mingw-w64-crt/testcases/t_safe_flush.c
index f587338..5e617fa 100644
--- a/mingw-w64-crt/testcases/t_safe_flush.c
+++ b/mingw-w64-crt/testcases/t_safe_flush.c
@@ -14,7 +14,7 @@
 
 CRITICAL_SECTION cs;
 
-static unsigned int __stdcall thread_main(void *user_data) {
+static DWORD WINAPI thread_main(LPVOID user_data) {
     HANDLE handle_event = (HANDLE) user_data;
 
     /* This thread acquires a critical section and then
@@ -34,7 +34,7 @@
     HANDLE handle_event;
 
     assert(handle_event = CreateEvent(NULL, TRUE, FALSE, NULL));
-    assert(_beginthreadex(NULL, 0, thread_main, handle_event, 0, NULL) != 0);
+    assert(CreateThread(NULL, 0, thread_main, handle_event, 0, NULL) != NULL);
     assert(WaitForSingleObject(handle_event, INFINITE) == WAIT_OBJECT_0);
     assert(CloseHandle(handle_event));
 }