Fix for bug #31781: multi-table UPDATE with temp-pool enabled fails

                    with errno 17

my_create() did not perform any checks for the case when a file is
successfully created by a call to open(), but the call to
my_register_filename() later fails because the number of open files
has exceeded the my_open_files limit. This can happen on platforms 
which do not have getrlimit(), and hence we do not know the real limit
for open files. In such a case an error was returned to a caller
although the file has actually been created. Since callers assume
my_create() to return an error only when it failed to create a file,
they did not perform any cleanups, leaving an 'orphaned' file on the
file system.

Fixed by adding a check for the above case to my_create() and ensuring
the newly created file is deleted before returning an error.

Creating a deterministic test case in the test suite is impossible,
because the exact steps required to reproduce the above situation
depend on the platform and/or environment (OS per-user limits, queries
executed by previous tests, startup parameters). The patch was
manually tested on Windows using examples posted in the bug report.

mysys/my_create.c

@@ -35,7 +35,7 @@
 File my_create(const char *FileName, int CreateFlags, int access_flags,
 	       myf MyFlags)
 {
-  int fd;
+  int fd, rc;
   DBUG_ENTER("my_create");
   DBUG_PRINT("my",("Name: '%s' CreateFlags: %d  AccessFlags: %d  MyFlags: %d",
 		   FileName, CreateFlags, access_flags, MyFlags));
@@ -60,6 +60,20 @@ File my_create(const char *FileName, int CreateFlags, int access_flags,
   fd = open(FileName, access_flags);
 #endif
 
-  DBUG_RETURN(my_register_filename(fd, FileName, FILE_BY_CREATE,
-				   EE_CANTCREATEFILE, MyFlags));
+  rc= my_register_filename(fd, FileName, FILE_BY_CREATE,
+                           EE_CANTCREATEFILE, MyFlags);
+  /*
+    my_register_filename() may fail on some platforms even if the call to
+    *open() above succeeds. In this case, don't leave the stale file because
+    callers assume the file to not exist if my_create() fails, so they don't
+    do any cleanups.
+  */
+  if (unlikely(fd >= 0 && rc < 0))
+  {
+    int tmp= my_errno;
+    my_delete(FileName, MyFlags);
+    my_errno= tmp;
+  }
+  
+  DBUG_RETURN(rc);
 } /* my_create */