vendor/bc: import version 6.2.0
This is a production release with a new feature and a few bug fixes.
The bug fixes include:
- A crash when bc and dc are built using editline, but history is not activated.
- A missing local in the uint*() family of functions in the extended math library.
- A failure to clear the tail call list in dc on error.
- A crash when attempting to swap characters in command-line history when no characters exist.
- SIGWINCH was activated even when history was not.
The new feature is that stack traces are now given for runtime errors.
In debug mode, the C source file and line of errors are given as well.