Don't interrupt core on riscv-test exit only on syscall

enable width to be 4 in elf2hex

Run it yourself if you modify configure.ac, and commit the configure script.

Build fix for FreeBSD

Add support for pkg-config

Despite having only a slightly different autoconf version (2.68 vs
2.69), this changes HAVE_FESVR to FESVR_ENABLED.  I didn't see any
uses of this anywhere, so I don't think it matters, but it does worry
me a bit.

This allows pkg-config to find fesvr.

Change the behavior of the DESTDIR make variable

DESTDIR is a common make idiom.  As per the GNU coding standards

  https://www.gnu.org/prep/standards/html_node/DESTDIR.html

  "DESTDIR is a variable prepended to each installed target file, like
  this:

  $(INSTALL_PROGRAM) foo $(DESTDIR)$(bindir)/foo
  $(INSTALL_DATA) libfoo.a $(DESTDIR)$(libdir)/libfoo.a

  The DESTDIR variable is specified by the user on the make command
  line as an absolute file name. For example:

  make DESTDIR=/tmp/stage install

  DESTDIR should be supported only in the install* and uninstall*
  targets, as those are the only targets where it is useful.

  If your installation step would normally install /usr/local/bin/foo
  and /usr/local/lib/libfoo.a, then an installation invoked as in the
  example above would install /tmp/stage/usr/local/bin/foo and
  /tmp/stage/usr/local/lib/libfoo.a instead."

The current Makefile.in uses DESTDIR, but has a slightly non-standard
behavior: the target install location doesn't include "$prefix".  This
breaks package managers, because stuff ends up getting installed to
the wrong location.

Unfortunately the only way I can think of to fix this involves
silently changing the behavior of DESTDIR.  Hopefully nobody is using
it...?

Now all 12 CSR address bits are sent over the HTIF interface.

This simplifies the pk <-> fesvr ABI at the cost of requiring
POSIX 2008 compliance (e.g. Mac OS Yosemite or later).

This simulates a chroot jail for the target machine.
There are probably some lingering bugs.

can be built for one place and installed in another

these syscalls will be available in osx 10.10

syscalls added (openat, access, accessat, faccessat, etc.)

Use __thread for compatibility with gcc <= 4.7.