vendor/bc: import version 6.3.1

This version adds a command to dc to query whether extended registers
are enabled or not.

(cherry picked from commit 103d7cdfb7435591049413e1bc39482cb316efb7)

contrib/bc: import version 6.5.0

This release that fixes an infinite loop bug in the (non-standard)
extended math library functions root() and cbrt(), fixes a bug with
BC_LINE_LENGTH=0, and adds the fib() function to the extended math
library to calculate Fibonacci numbers.

(cherry picked from commit 8c48f4c5377ddc3dc55388f181f23111145f7099)

contrib/bc: upgrade to version 6.6.0

This update removes printing of a leading zero in scientific or
engineering output modes (which are an extended feature of this
implementation).

(cherry picked from commit 76238846ad3e9e271a3d1f792f72beab727fd153)