Reduce the difference to NetBSD.

 * Stop pretending we support anything other than ELF by removing code
   surrounded by #ifdef __ELF__ ... #endif.
 * Remove _JB_MAGIC_SETJMP and _JB_MAGIC__SETJMP, they are defined in
   setjmp.h, which is able to be included from asm.
 * Fix the spelling of dependent.
 * Rename END _END and add END and ASEND to complement ENTRY and ASENTRY
   respectively
 * Add macros to simplify accessing the Global Offset Table, some of these
   will be used in the upcoming update to the setjmp functions.
Add a new knob WITH_DEBUG_FILES to control the building of standalone
debug files for userland programs and libraries.  The "-g" debug flag
is automatically applied when WITH_DEBUG_FILES is set.

The debug files are now named ${prog}.debug and ${shlib}.debug for
consistency with other systems and documentation.  In addition they are
installed under /usr/lib/debug, to simplify the process of installing
them if needed after a crash.  Users of bsd.{prog,lib}.mk outside of the
base system place the standalone debug files in a .debug subdirectory.
GDB automatically searches both of these directories for standalone
debug files.

Thanks to everyone who contributed changes, review, and testing during
development.
Add WITH_DEBUG_FILES

makeman currently generates a src.conf that claims every option also
enforces WITHOUT_BIND_UTILS, so I applied this section by hand.
Finish pulling in the NetBSD setjmp/longjmp updates on ARM.

Store/restore the VFP registers in setjmp/longjmp on ARM EABI if VFP is
enabled in the kernel. It checks the hw.floatingpoint sysctl to see if
floating-point is available and uses this to determine if it should store
them. If it does it uses a different magic value so longjmp is able to know
if it should load them.