windows: use _strdup() instead of strdup() where missing

To replace deprecated `strdup()` CRT calls with the recommended
`_strdup()`.

Refs:
https://learn.microsoft.com/cpp/c-runtime-library/reference/strdup-wcsdup
https://learn.microsoft.com/cpp/c-runtime-library/reference/strdup-wcsdup-mbsdup

Closes #19794

docs/examples/block_ip.c

@@ -38,12 +38,6 @@ int main(void)
 }
 #else
 
-#ifdef _MSC_VER
-#ifndef _CRT_NONSTDC_NO_DEPRECATE
-#define _CRT_NONSTDC_NO_DEPRECATE  /* for strdup() */
-#endif
-#endif
-
 #ifdef _WIN32
 #if !defined(_WIN32_WINNT) || _WIN32_WINNT < 0x0600
 #undef _WIN32_WINNT
@@ -52,6 +46,7 @@ int main(void)
 #include <winsock2.h>
 #include <ws2tcpip.h>
 #include <windows.h>
+#define strdup _strdup
 #else
 #include <sys/types.h>
 #include <sys/socket.h>

lib/curl_setup.h

@@ -91,8 +91,7 @@
 #pragma warning(disable:4127)
 /* Avoid VS2005 and upper complaining about portable C functions. */
 #ifndef _CRT_NONSTDC_NO_DEPRECATE  /* mingw-w64 v2+. MS SDK ~10+/~VS2017+. */
-#define _CRT_NONSTDC_NO_DEPRECATE  /* for close(), fileno(), strdup(),
-                                      unlink(), etc. */
+#define _CRT_NONSTDC_NO_DEPRECATE  /* for close(), fileno(), unlink(), etc. */
 #endif
 #ifndef _CRT_SECURE_NO_WARNINGS
 #define _CRT_SECURE_NO_WARNINGS  /* for getenv(), gmtime(), strcpy(),

lib/easy.c

@@ -103,7 +103,11 @@ static curl_simple_lock s_lock = CURL_SIMPLE_LOCK_INIT;
  * so the callback pointer is initialized correctly.
  */
 #ifdef HAVE_STRDUP
+#ifdef _WIN32
+#define system_strdup _strdup
+#else
 #define system_strdup strdup
+#endif
 #else
 #define system_strdup Curl_strdup
 #endif

tests/libtest/memptr.c

@@ -36,7 +36,11 @@
 curl_malloc_callback Curl_cmalloc = (curl_malloc_callback)malloc;
 curl_free_callback Curl_cfree = (curl_free_callback)free;
 curl_realloc_callback Curl_crealloc = (curl_realloc_callback)realloc;
+#ifdef _WIN32
+curl_strdup_callback Curl_cstrdup = (curl_strdup_callback)_strdup;
+#else
 curl_strdup_callback Curl_cstrdup = (curl_strdup_callback)strdup;
+#endif
 curl_calloc_callback Curl_ccalloc = (curl_calloc_callback)calloc;
 
 #if defined(_MSC_VER) && defined(_DLL)

tests/server/first.h

@@ -69,6 +69,10 @@ extern const struct entry_s s_entries[];
 #  define snprintf _snprintf
 #endif
 
+#ifdef _WIN32
+#  define strdup _strdup
+#endif
+
 #ifdef _WIN32
 #  define CURL_STRNICMP(p1, p2, n) _strnicmp(p1, p2, n)
 #elif defined(HAVE_STRCASECMP)