lang/gcc-aux: Fix symbolic trace on FreeBSD

Recent gcc creates debug information in dwarf4 format, something that
the base version of addr2line on FreeBSD cannot understand.  When the
compiler requires binutils from ports to build, then ensure the
symbolic tracing code also uses addr2line from the same binutils (which
is already available due to RUN_DEPENDS requirements).  Since DragonFly
3.6 and lower are no longer officially supported, this change only
affects FreeBSD, but it affects all supported releases.  The conditional
code for DragonFly 3.6 has been removed while here.

Reported by:	Natacha Porte
PR:		195465
Add a note about what went wrong yesterday.

Sponsored by:	Absolight
Fixup the makewhatis errors.

Sponsored by:	Absolight