devel/freebsd-gcc6: update to GCC 6.5.0.

[jhb]

Summary

Take maintainership.

Test Plan

• built mips64, aarch64, and i386 worlds with cross toolchain

[lwhsu]

BTW, I would suggest doing similar improvements like devel/binutils to have "native" FLAVOR, now the default is aarch64.

ref: https://lists.freebsd.org/pipermail/freebsd-toolchain/2019-November/005074.html

[jhb]

In D22506#492281, @lwhsu wrote:

BTW, I would suggest doing similar improvements like devel/binutils to have "native" FLAVOR, now the default is aarch64.

ref: https://lists.freebsd.org/pipermail/freebsd-toolchain/2019-November/005074.html

A native flavor doesn't make sense for this port though, that would mean we would have a 'freebsd-gcc6' package, but we have that already in base/gcc which installs to /usr, etc. Perhaps we can merge base/gcc into this someday, but that may not work well. In particular, you can't build base/gcc in poudriere because it writes to /usr which fails since the jail is mounted read-only and only permits writes to LOCALBASE. Also, base/gcc uses an extra patch and has some other settings to support cross-building, etc. I could perhaps make the default flavor be ${ARCH} instead of the first flavor in the list so that by default you get the 'amd64-gcc' package, but that would just mean that 'freebsd-gcc6' would alias 'freebsd-gcc6@amd64'. Note that this is always the case with flavors that the default flavor aliases with the base package name.