Divorce MK_GDB from MK_BINUTILS.

[jhb]

Summary

This permits legacy GDB to still be built and installed if
WITHOUT_BINUTILS is set (e.g. if base/binutils is installed).

Test Plan

• used in an amd64 VM using base/* as the toolchain to still get a /usr/libexec/kgdb for crashinfo
• passed make tinderbox

[emaste]

You'll want to update the WITH_/WITHOUT_BINUTILS files too

[emaste]

Modulo the WITH/WITHOUT updates, looks good

[jhb]

In D19480#417000, @emaste wrote:

You'll want to update the WITH_/WITHOUT_BINUTILS files too

Hmm, I looked at those but they don't reference gdb at all. However, regenerating src.conf.5 did generate a diff I'll upload in a sec.

[jhb]

• Regen src.conf.5.

[emaste]

In D19480#417046, @jhb wrote:

Hmm, I looked at those but they don't reference gdb at all. However, regenerating src.conf.5 did generate a diff I'll upload in a sec.

Oh, I thought they made reference to gdb, but you're right, they already describe only the binutils not controlled by MK_GDB.