bhyve: Add arm64 support to the gdb stub

- Add -G to the arm64 getopt handler.
- Add static register definitions and extensible XML definitions.
- Provide definitions for MD bits such as breakpoint

bhyve: Add arm64 support to the gdb stub

- Add -G to the arm64 getopt handler.
- Add static register definitions and extensible XML definitions.
- Provide definitions for MD bits such as breakpoint encoding and
length.
- Ensure that bhyve re-injects breakpoint exceptions that it is not
responsible for.

Reviewed by: andrew
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D44740

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bhyve/gdb: Avoid rebuilding target.xml for install targets

Otherwise it's impossible to install from a read-only objdir.

Fixes: f81cdf24ba54 ("bhyve: Add support for XML register definitions")
Repo

bhyve/gdb: Avoid rebuilding target.xml for install targets

Otherwise it's impossible to install from a read-only objdir.

Fixes: f81cdf24ba54 ("bhyve: Add support for XML register definitions")
Reported by: olivier

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bhyve: Add support for XML register definitions

This is useful for exposing additional registers to debuggers. For
instance, control registers are now available on amd64 when using gdb to
debug a g

bhyve: Add support for XML register definitions

This is useful for exposing additional registers to debuggers. For
instance, control registers are now available on amd64 when using gdb to
debug a guest.

The stub indicates support by including the string
"qXfer:features:read+" in its feature list. The debugger queries for
target descriptions by sending the query "qXfer:features:read:" followed
by a file path.

The XML definitions are copied from QEMU and installed to
/usr/share/bhyve/gdb.

Note that we currently don't handle the SIMD registers at all, since
that's of somewhat limited utility (for me at least) and since that
requires new ioctls to fetch the register values.

Reviewed by: jhb
MFC after: 2 weeks
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D43666

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