Comment 5 for bug 1197049

I did not trace the code, but I see that src/3rdparty/sqlite/sqlite3.c is defining its own tempfile handling (I have no idea why, but there you go). There is code to handle TMPDIR throughout. I also found this:
  /*
  ** PRAGMA temp_store_directory
  ** PRAGMA temp_store_directory = ""|"directory_name"
  **
  ** Return or set the local value of the temp_store_directory flag. Changing
  ** the value sets a specific directory to be used for temporary files.
  ** Setting to a null string reverts to the default temporary directory search.
  ** If temporary directory is changed, then invalidateTempStorage.
  **
  */

I guess if we set temp_store_directory to null, things would work (I don't know where you would set that). Keep in mind, this is only a super-cursory look at the code to affirm that this bug should be able to be fixed by a minor tweak somewhere.