math/gh-bc: update to version 7.1.0

This fixes a few bugs:

• Improper response to double SIGINT with editline.
• Not letting libedit handle terminal size changes.
• A dc crash from improperly handling an error.
• A duplicate check for reference arrays.
• Build failures with GCC 15.

It also has a performance increase in the band() function and others
in the math library.