curlx: promote Curl_fseeko() to curlx_fseek(), use it in src

- tool_formparse: replace truncated `fseek` with `curlx_fseek`.
- tool_operate: replace truncated `fseek` with `curlx_fseek`.
- tool_paramhlp: replace local duplicate `myfseek`, with `curlx_fseek`.

Follow-up to 4fb12f2891 #19100

Closes #19107

lib/curlx/fopen.c

@@ -32,9 +32,23 @@
 
 #include "../curl_setup.h"
 
+#include "fopen.h"
+
+int curlx_fseek(void *stream, curl_off_t offset, int whence)
+{
+#if defined(_WIN32) && defined(USE_WIN32_LARGE_FILES)
+  return _fseeki64(stream, (__int64)offset, whence);
+#elif defined(HAVE_FSEEKO) && defined(HAVE_DECL_FSEEKO)
+  return fseeko(stream, (off_t)offset, whence);
+#else
+  if(offset > LONG_MAX)
+    return -1;
+  return fseek(stream, (long)offset, whence);
+#endif
+}
+
 #if defined(_WIN32) && !defined(UNDER_CE)
 
-#include "fopen.h"
 #include "multibyte.h"
 
 /* declare GetFullPathNameW for mingw-w64 UWP builds targeting old windows */

lib/curlx/fopen.h

@@ -32,6 +32,8 @@
 #include <fcntl.h>  /* for open() and attributes */
 #endif
 
+int curlx_fseek(void *stream, curl_off_t offset, int whence);
+
 #if defined(_WIN32) && !defined(UNDER_CE)
 FILE *curlx_win32_fopen(const char *filename, const char *mode);
 int curlx_win32_stat(const char *path, struct_stat *buffer);

lib/formdata.c

@@ -37,6 +37,7 @@ struct Curl_easy;
 #include "sendf.h"
 #include "strdup.h"
 #include "rand.h"
+#include "curlx/fopen.h"
 #include "curlx/warnless.h"
 
 /* The last 2 #include files should be in this order */
@@ -860,7 +861,7 @@ CURLcode Curl_getformdata(CURL *data,
 #endif
             result = curl_mime_data_cb(part, (curl_off_t) -1,
                                        (curl_read_callback) fread,
-                                       Curl_fseeko,
+                                       curlx_fseek,
                                        NULL, (void *) stdin);
 #if defined(__clang__) && __clang_major__ >= 16
 #pragma clang diagnostic pop

lib/mime.c

@@ -271,19 +271,6 @@ static char *Curl_basename(char *path)
 #define basename(x)  Curl_basename((x))
 #endif
 
-int Curl_fseeko(void *stream, curl_off_t offset, int whence)
-{
-#if defined(_WIN32) && defined(USE_WIN32_LARGE_FILES)
-  return _fseeki64(stream, (__int64)offset, whence);
-#elif defined(HAVE_FSEEKO) && defined(HAVE_DECL_FSEEKO)
-  return fseeko(stream, (off_t)offset, whence);
-#else
-  if(offset > LONG_MAX)
-    return -1;
-  return fseek(stream, (long)offset, whence);
-#endif
-}
-
 
 /* Set readback state. */
 static void mimesetstate(struct mime_state *state,
@@ -750,7 +737,7 @@ static int mime_file_seek(void *instream, curl_off_t offset, int whence)
   if(mime_open_file(part))
     return CURL_SEEKFUNC_FAIL;
 
-  return Curl_fseeko(part->fp, offset, whence) ?
+  return curlx_fseek(part->fp, offset, whence) ?
     CURL_SEEKFUNC_CANTSEEK : CURL_SEEKFUNC_OK;
 }
 

lib/mime.h

@@ -138,7 +138,6 @@ CURLcode Curl_mime_add_header(struct curl_slist **slp, const char *fmt, ...)
                                     !defined(CURL_DISABLE_IMAP))
 
 /* Prototypes. */
-int Curl_fseeko(void *stream, curl_off_t offset, int whence);
 void Curl_mime_initpart(struct curl_mimepart *part);
 void Curl_mime_cleanpart(struct curl_mimepart *part);
 CURLcode Curl_mime_duppart(struct Curl_easy *data,