[MSVCRT_SHARED] Implement TLS support for ucrtbase

dll/win32/msvcrt/CMakeLists.txt

···
 add_library(msvcrt_shared
     ${SHARED_SOURCE}
     ${msvcrt_shared_asm}
+    reactos/ucrt_tls_sup.c
 )
 
 target_compile_definitions(msvcrt_shared PRIVATE _MSVCR_VER=0 __UCRTSUPPORT__)

dll/win32/msvcrt/reactos/ucrt_tls_sup.c

···
+/*
+ * PROJECT:     ReactOS msvcrt
+ * LICENSE:     MIT (https://spdx.org/licenses/MIT)
+ * PURPOSE:     TLS support code for use with ucrtbase
+ * COPYRIGHT:   Copyright 2025 Timo Kreuzer <[e-mail]>
+ */
+
+#include <process.h>
+#include <assert.h>
+#include "msvcrt.h"
+#include "wine/debug.h"
+
+WINE_DEFAULT_DEBUG_CHANNEL(msvcrt);
+
+DWORD msvcrt_tls_index;
+
+BOOL msvcrt_init_tls(void)
+{
+    msvcrt_tls_index = TlsAlloc();
+    if (msvcrt_tls_index == TLS_OUT_OF_INDEXES)
+    {
+        ERR("TlsAlloc() failed!\n");
+        return FALSE;
+    }
+
+    return TRUE;
+}
+
+BOOL msvcrt_free_tls(void)
+{
+    if (!TlsFree(msvcrt_tls_index))
+    {
+        ERR("TlsFree() failed!\n");
+        return FALSE;
+    }
+
+    return TRUE;
+}
+
+void msvcrt_free_tls_mem(void)
+{
+    thread_data_t *tls = TlsGetValue(msvcrt_tls_index);
+    if (tls)
+    {
+        free(tls->efcvt_buffer);
+        assert(tls->asctime_buffer == NULL);
+        assert(tls->wasctime_buffer == NULL);
+        assert(tls->strerror_buffer == NULL);
+        assert(tls->wcserror_buffer == NULL);
+        assert(tls->time_buffer == NULL);
+        assert(tls->tmpnam_buffer == NULL);
+        assert(tls->wtmpnam_buffer == NULL);
+        assert(tls->locinfo == NULL);
+        assert(tls->mbcinfo == NULL);
+        HeapFree(GetProcessHeap(), 0, tls);
+    }
+}
+
+thread_data_t *CDECL msvcrt_get_thread_data(void)
+{
+    thread_data_t *ptr;
+    DWORD err = GetLastError();  /* need to preserve last error */
+
+    ptr = TlsGetValue(msvcrt_tls_index);
+    if (ptr == NULL)
+    {
+        ptr = HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, sizeof(*ptr));
+        if (ptr == NULL)
+            exit(_RT_THREAD);
+
+        if (!TlsSetValue(msvcrt_tls_index, ptr))
+            exit(_RT_THREAD);
+
+        ptr->tid = GetCurrentThreadId();
+        ptr->handle = INVALID_HANDLE_VALUE;
+        ptr->random_seed = 1;
+    }
+
+    SetLastError(err);
+    return ptr;
+}