New GDB/MI command "-info-gdb-mi-command"

This patch adds a new GDB/MI command meant for graphical frontends
trying to determine whether a given GDB/MI command exists or not.

Examples:

    -info-gdb-mi-command unsupported-command
    ^done,command={exists="false"}
    (gdb)
    -info-gdb-mi-command symbol-list-lines
    ^done,command={exists="true"}
    (gdb)

At the moment, this is the only piece of information that this
command returns.

Eventually, and if needed, we can extend it to provide
command-specific pieces of information, such as updates to
the command's syntax since inception.  This could become,
for instance:

    -info-gdb-mi-command symbol-list-lines
    ^done,command={exists="true",features=[]}
    (gdb)
    -info-gdb-mi-command catch-assert
    ^done,command={exists="true",features=["conditions"]}

In the first case, it would mean that no extra features,
while in the second, it announces that the -catch-assert
command in this version of the debugger supports a feature
called "condition" - exact semantics to be documented with
combined with the rest of the queried command's documentation.

But for now, we start small, and only worry about existance.
And to bootstrap the process, I have added an entry in the
output of the -list-features command as well ("info-gdb-mi-command"),
allowing the graphical frontends to go through the following process:

  1. Send -list-features, collect info from there as before;
  2. Check if the output contains "info-gdb-mi-command".
     If it does, then support for various commands can be
     queried though -info-gdb-mi-command. Newer commands
     will be expected to always be checked via this new
     -info-gdb-mi-command.

gdb/ChangeLog:

        * mi/mi-cmds.h (mi_cmd_info_gdb_mi_command): Declare.
        * mi/mi-cmd-info.c (mi_cmd_info_gdb_mi_command): New function.
        * mi/mi-cmds.c (mi_cmds): Add -info-gdb-mi-command command.
        * mi/mi-main.c (mi_cmd_list_features): Add "info-gdb-mi-command"
        field to output of "-list-features".

        * NEWS: Add entry for new -info-gdb-mi-command.

gdb/doc/ChangeLog:

        * gdb.texinfo (GDB/MI Miscellaneous Commands): Document
        the new -info-gdb-mi-command GDB/MI command.  Document
        the meaning of "-info-gdb-mi-command" in the output of
        -list-features.

gdb/testsuite/ChangeLog:

        * gdb.mi/mi-i-cmd.exp: New file.
Add "undefined-command" error code at end of ^error result...

... when trying to execute an undefined GDB/MI command. When trying
to execute a GDB/MI command which does not exist, the current error
result record looks like this:

    -unsupported
    ^error,msg="Undefined MI command: unsupported"

The only indication that the command does not exist is the error
message. It would be a little fragile for a consumer to rely solely
on the contents of the error message in order to determine whether
a command exists or not.

This patch improves the situation by adding concept of error
code, starting with one well-defined error code ("undefined-command")
identifying errors due to a non-existant command. Here is the new
output:

    -unsupported
    ^error,msg="Undefined MI command: unsupported",code="undefined-command"

This error code is only displayed when the corresponding error
condition is met. Otherwise, the error record remains unchanged.
For instance:

    -symbol-list-lines foo.adb
    ^error,msg="-symbol-list-lines: Unknown source file name."

For frontends to be able to know whether they can rely on this
variable, a new entry "undefined-command-error-code" has been
added to the "-list-features" command.  Another option would be
to always generate an error="..." variable (for the default case,
we could decide for instance that the error code is the empty string).
But it seems more efficient to provide that info in "-list-features"
and then only add the error code when meaningful.

gdb/ChangeLog:

        (from Pedro Alves  <palves@redhat.com>)
        (from Joel Brobecker  <brobecker@adacore.com>)
        * exceptions.h (enum_errors) <UNDEFINED_COMMAND_ERROR>: New enum.
        * mi/mi-parse.c (mi_parse): Throw UNDEFINED_COMMAND_ERROR instead
        of a regular error when the GDB/MI command does not exist.
        * mi/mi-main.c (mi_cmd_list_features): Add
        "undefined-command-error-code".
        (mi_print_exception): Print an "undefined-command"
        error code if EXCEPTION.ERROR is UNDEFINED_COMMAND_ERROR.
        * NEWS: Add entry documenting the new "code" variable in
        "^error" result records.

gdb/doc/ChangeLog:

        * gdb.texinfo (GDB/MI Result Records): Fix the syntax of the
        "^error" result record concerning the error message.  Document
        the error code that may also be part of that result record.
        (GDB/MI Miscellaneous Commands): Document the
        "undefined-command-error-code" element in the output of
        the "-list-features" GDB/MI command.

gdb/testsuite/ChangeLog:

        * gdb.mi/mi-undefined-cmd.exp: New testcase.
PowerPC64 linking of --just-symbols objects (klibc)

With -mcmodel=medium we can't assume that a -R object doesn't use
toc-relative addressing if there's no toc.  Lots of things are
accessed via r2, not just the toc/got section.  Also, testing for
.opd is plain wrong for ELFv2.

	* elf64-ppc.c (ppc64_elf_link_just_syms): Remove .got check.
	Handle ELFv2.
Remove all trailing spaces in mi/mi-main.c.

No code change, just a mechanical cleanup.

gdb/ChangeLog:

        * mi/mi-main.c: Remove trailing spaces throughout.
Remove "ada-exceptions" from -list-features output.

Now that the -info-gdb-mi-command is available, there is no need for
this entry. The entry and associated new commands were added recently
enough that no front-end out there should be depending on it yet.

gdb/ChangeLog:

        * mi/mi-main.c (mi_cmd_list_features): Remove "ada-exceptions".

gdb/doc/ChangeLog:

        * gdb.texinfo (GDB/MI Miscellaneous Commands): Remove the
        documentation of the "ada-exceptions" entry.
MAINTAINERS (Write After Approval): Add myself to the list.
Resurrect gdb-add-index as a contrib script

This includes changes made in Fedora's gdb packaging[1], Doug's
robustness patch[2] from before gdb-add-index was dropped, some
corrections, and some more changes Doug accumulated in the
meantime[3].

[1]: http://pkgs.fedoraproject.org/cgit/gdb.git/log/gdb-gdb-add-index-script.patch?id=fe74423b0812bae6d7bb027584e401a2ac37d24d
[2]: https://sourceware.org/ml/gdb-patches/2010-09/msg00130.html
[3]: https://sourceware.org/ml/gdb-patches/2013-11/msg00297.html

It would be a good idea to mention the existance of this script
in (info "(gdb) Index Files"), but I'm boycotting invariant
sections/cover texts because non-free docs are a PITA, so somebody
else would need to do that.

Summary of previous activity:

97924a9 Actual removal
c29c521 Attempted removal (accidentally left gdb-add-index.sh in place)
c2bbed2 Addition
More PowerPC64 ELFv2 --just-symbols fixes

I don't know what I was thinking here to omit the save of r2.
Possibly I was looking at -msave-toc-indirect code at the time, where
r2 is saved in the function prologue.

	* elf64-ppc.c (ppc_build_one_stub <ppc_stub_plt_branch_r2off>):
	Don't omit saving of r2 for ELFv2.  Don't addi 2,2,0.
	(ppc_size_one_stub <ppc_stub_plt_branch_r2off>): Adjust to suit.