Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

- Make sure to set an error code when trying to obtain a data descriptor for
a section of type SHT_NULL.
- Update the man page to reflect the fact that elf_getdata() and
elf_rawdata() may return with an error of ELF_E_SECTION.

PR: bin/175491
Approved by: emaste (co-mentor)
MFC after: 1 week

General mdoc(7) and typo fixes.

PR: 167734
Submitted by: Nobuyuki Koganemaru (kogane!jp.freebsd.org)
MFC after: 3 days

Remove trailing whitespace per mdoc lint warning

Disussed with: gavin
No objection from: doc
Approved by: joel
MFC after: 3 days

Document the behavior of `elf_getdata()` and `elf_rawdata()` with
zero-sized ELF sections.

Obtained from: elftoolchain

Add a cross-reference to `elf_rawfile(3)`.

Obtained from: elftoolchain
MFC after: 1 month

- Correctly handle sections of type SHT_NOBITS. For these sections:
- elf_getdata() and elf_rawdata() should return an "Elf_Data" structure
that has its "d_buf" member set to NULL and "d_size" member set to
the nominal 'size' of the section. [1]
- Update the manual page for these functions.
- Fix a memory leak in an error handling path inside elf_getdata().
- Use _libelf_allocate_data() in elf_newdata() for consistency.

Obtained from: elftoolchain
MFC after: 1 month

mdoc: order prologue macros consistently by Dd/Dt/Os

Although groff_mdoc(7) gives another impression, this is the ordering
most widely used and also required by mdocml/mandoc.

Reviewed by: ru
Approved by: philip, ed (mentors)

Fix minor formatting issues:

- make document title match filename;
- remove hard sentence breaks, whitespace at EOL, and double whitespace;
- sort SEE ALSO xrefs, adding missing section numbers;
- fix a misspelled macro name.

MFP4: Add an implementation of the ELF(3) and GELF(3) API set.

Bump __FreeBSD_version.

Reviewed by: jb