Add a features.h to auto enable _DEFAULT_SOURCE

Unless __STRICT_ANSI__ is defined (as it is when running the compiler in
--std=c89 or --std=c99, but not when running it without any specific
args), we can enable these by default and behave like most other
systems. I don't know why no one has done this yet despite suggesting it
multiple times and people prefer to #define _BSD_SOURCE manually
everywhere.

Remove all places in our Jamfiles and sources where it had been defined.
_DEFAULT_SOURCE is now enabled by default for all sources of Haiku, since we
let the compiler use GNU extensions (no strict C standard specified on
command line)

Use _DEFAULT_SOURCE as the define name to match current versions of
glibc. Enable it if _BSD_SOURCE is #defined in compiler flags, for
backward compatibility.

Change-Id: I6db04da5f6db437723cdfba3478f5094a69d7727
Reviewed-on: https://review.haiku-os.org/c/1633
Reviewed-by: Jérôme Duval <jerome.duval@gmail.com>

Protect all BSD extensions with _BSD_SOURCE

* Do not define the symbols by default, as they are not in the default
libraries.
* Adjust jamfiles of all code using BSD extensions to define
_BSD_SOURCE.
* This makes Haiku slightly more compliant to standard C/POSIX.

Updated posix headers to remove commas from copyright line, to match the preferred coding guidelines.
Cleaned up some header style violations, making sure there are two blank lines after the header guards.
This fixes the bsd header part of #2191.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@39291 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Added BSD specific errno.h for EDOOFUS (yeah, I know, great error code...)
* Added sigmask() macro.
* Fixed libutil.h I broke yesterday: it's thought to add functions only if
you've included some other headers before; added the correct header guard
we're using for our sys/param.h.
* Added pidfile.c to the build.
* Fixed warning in realhostname.c, and pidfile.c.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@23840 a95241bf-73f2-0310-859d-f6bbb57e9c96

Protect all BSD extensions with _BSD_SOURCE

* Do not define the symbols by default, as they are not in the default
libraries.
* Adjust jamfiles of all code using BSD extensions to define
_BSD_SOURCE.
* This makes Haiku slightly more compliant to standard C/POSIX.

Updated posix headers to remove commas from copyright line, to match the preferred coding guidelines.
Cleaned up some header style violations, making sure there are two blank lines after the header guards.
This fixes the bsd header part of #2191.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@39291 a95241bf-73f2-0310-859d-f6bbb57e9c96

* Added BSD specific errno.h for EDOOFUS (yeah, I know, great error code...)
* Added sigmask() macro.
* Fixed libutil.h I broke yesterday: it's thought to add functions only if
you've included some other headers before; added the correct header guard
we're using for our sys/param.h.
* Added pidfile.c to the build.
* Fixed warning in realhostname.c, and pidfile.c.


git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@23840 a95241bf-73f2-0310-859d-f6bbb57e9c96