vendor/bc: MFC upgrade from version 6,6.0 to 6.7.5

This is a squashed updated consisting of:

vendor/bc: upgrade to version 6.7.2

This update improves the implementation of the power function p() and
adds 3 new functions to the extended math library: min(), max(), and
i2rand().

(cherry picked from commit aa339f1d5df9e38f36a34eb522355c4eebcae6c4)

vendor/bc: upgrade to version 6.7.4

Documentation updates only, no functional changes to the software.

(cherry picked from commit e6857bd4d7b4bf39ea32b9dcd34f8371164c356e)

vendor/bc: upgrade to version 6.7.5

This update fixes a bug that line breaks in printed numbers may not
match the line length set by the user. The value is printed correctly,
just not split as specified in some situations.

(cherry picked from commit f4fbc49d201f81c481a33fac6ba28e19faf96260)