build: tidy up local lseek() mappings

- stop redefining system symbol `lseek`, by introducing `curl_lseek()`.
- handle AmigaOS quirk within the macro mapping.
- add missing parenthesis to `LSEEK_ERROR` values.
- tool_util: use curl `lseek` macros in `tool_ftruncate64()`.
- move `LSEEK_ERROR` to right-hand side of if expressions.
- checksrc: disallow direct uses of `_lseeki64`, `llseek`, `lseek`.

Closes #20488

src/tool_cb_see.c

@@ -61,13 +61,13 @@ int tool_seek_cb(void *userdata, curl_off_t offset, int whence)
       /* this code path does not support other types */
       return CURL_SEEKFUNC_FAIL;
 
-    if(LSEEK_ERROR == lseek(per->infd, 0, SEEK_SET))
+    if(curl_lseek(per->infd, 0, SEEK_SET) == LSEEK_ERROR)
       /* could not rewind to beginning */
       return CURL_SEEKFUNC_FAIL;
 
     while(left) {
       long step = (left > OUR_MAX_SEEK_O) ? OUR_MAX_SEEK_L : (long)left;
-      if(LSEEK_ERROR == lseek(per->infd, step, SEEK_CUR))
+      if(curl_lseek(per->infd, step, SEEK_CUR) == LSEEK_ERROR)
         /* could not seek forwards the desired amount */
         return CURL_SEEKFUNC_FAIL;
       left -= step;
@@ -76,11 +76,7 @@ int tool_seek_cb(void *userdata, curl_off_t offset, int whence)
   }
 #endif
 
-#ifdef __AMIGA__
-  if(LSEEK_ERROR == lseek(per->infd, (off_t)offset, whence))
-#else
-  if(LSEEK_ERROR == lseek(per->infd, offset, whence))
-#endif
+  if(curl_lseek(per->infd, offset, whence) == LSEEK_ERROR)
     /* could not rewind, the reason is in errno but errno is just not portable
        enough and we do not actually care that much why we failed. We will let
        libcurl know that it may try other means if it wants to. */

src/tool_util.c

@@ -86,7 +86,7 @@ int tool_ftruncate64(int fd, curl_off_t where)
 {
   intptr_t handle = _get_osfhandle(fd);
 
-  if(_lseeki64(fd, where, SEEK_SET) < 0)
+  if(curl_lseek(fd, where, SEEK_SET) == LSEEK_ERROR)
     return -1;
 
   if(!SetEndOfFile((HANDLE)handle))