MFC 313407,313449: Copy ELF machine/flags from binaries to core dumps.

313407:
Copy the e_machine and e_flags fields from the binary into an ELF core dump.

In the kernel, cache the machine and flags fields from ELF header to use in
the ELF header of a core dump. For gcore, the copy these fields over from
the ELF header in the binary.

This matters for platforms which encode ABI information in the flags field
(such as o32 vs n32 on MIPS).

313449:
Trim trailing whitespace (mostly introduced in r313407).

Sponsored by: DARPA / AFRL

MFC 303002: Include process IDs in core dumps.

When threads were added to the kernel, the pr_pid member of the
NT_PRSTATUS note was repurposed to store LWP IDs instead of process
IDs. However, the process ID was no longer recorded in core dumps.
This change adds a pr_pid field to prpsinfo (NT_PRSINFO). Rather than
bumping the prpsinfo version number, note parsers can use the note's
payload size to determine if pr_pid is present.

MFC 302859: Include command line arguments in core dump process info.

Fill in pr_psargs in the NT_PRSINFO ELF core dump note with command
line arguments.

MFC 299458: Fix buffer overrun in gcore(1) NT_PRPSINFO

Use size of destination buffer, rather than a constant that may or may not
correspond to the source buffer, to restrict the length of copied strings. In
particular, pr_fname has 16+1 characters but MAXCOMLEN is 18+1.

Use strlcpy instead of strncpy to ensure the result is nul-terminated. This
seems to be what is expected of these fields.

MFC r302179:
gcore: Forward pending signals when detaching from the target.

MFC 269128:
Create 32-bit core files for 32-bit processes on 64-bit machines.
The 64-bit machine supported right now is amd64, but it's not too
hard to add powerpc64.

MFC 278761:
Include OBJT_PHYS VM objects in ELF core dumps. In particular this
includes the shared page allowing debuggers to use the signal trampoline
code to identify signal frames in core dumps.

MFC 274817,274878,276801,276840,278976:
Improve support for XSAVE with debuggers.
- Dump an NT_X86_XSTATE note if XSAVE is in use. This note is designed
to match what Linux does in that 1) it dumps the entire XSAVE area
including the fxsave state, and 2) it stashes a copy of the current
xsave mask in the unused padding between the fxsave state and the
xstate header at the same location used by Linux.
- Teach readelf() to recognize NT_X86_XSTATE notes.
- Change PT_GET/SETXSTATE to take the entire XSAVE state instead of
only the extra portion. This avoids having to always make two
ptrace() calls to get or set the full XSAVE state.
- Add a PT_GET_XSTATE_INFO which returns the length of the current
XSTATE save area (so the size of the buffer needed for PT_GETXSTATE)
and the current XSAVE mask (%xcr0).

MFC 269128:
Create 32-bit core files for 32-bit processes on 64-bit machines.
The 64-bit machine supported right now is amd64, but it's not too
hard to add powerpc64.

MFC 278761:
Include OBJT_PHYS VM objects in ELF core dumps. In particular this
includes the shared page allowing debuggers to use the signal trampoline
code to identify signal frames in core dumps.

MFC 274817,274878,276801,276840,278976:
Improve support for XSAVE with debuggers.
- Dump an NT_X86_XSTATE note if XSAVE is in use. This note is designed
to match what Linux does in that 1) it dumps the entire XSAVE area
including the fxsave state, and 2) it stashes a copy of the current
xsave mask in the unused padding between the fxsave state and the
xstate header at the same location used by Linux.
- Teach readelf() to recognize NT_X86_XSTATE notes.
- Change PT_GET/SETXSTATE to take the entire XSAVE state instead of
only the extra portion. This avoids having to always make two
ptrace() calls to get or set the full XSAVE state.
- Add a PT_GET_XSTATE_INFO which returns the length of the current
XSTATE save area (so the size of the buffer needed for PT_GETXSTATE)
and the current XSAVE mask (%xcr0).