ELF Tool Chain Code

Change Elftoolchain's command-line utilities to exit with a zero exit
status when their respective help options are specified.

Original patch by: Mark Johnston on -developers

Fix '-Wimplicit-fallthrough' warnings.

strings: fix style nits

Submitted by: Mariusz Zaborski <oshogbo@...>
Obtained from: FreeBSD r340746, r340750

strings: avoid unnecessary trip through handle_file for stdin

Obtained from: FreeBSD r312779

strings: fix exit status if a file before the last one fails

Previously a command like "strings f1 f2 f3" reported the exit status
based only on processing the last file.

As with GNU strings, report an error exit status if an error was
encountered processing any of the files. While here simplify the
exit status handling to just success (0) / failure (1).

Reviewed by: brooks@..., kaiw

Correct a variety of spelling errors

Submitted by: Pedro Giffuni

strings: Ensure that the value of the '-n' option is positive.

Remove <sys/cdefs.h> includes

The BSD header <sys/cdefs.h> is only used for the macros __BEGIN_DECLS
and __END_DECLS. musl libc does not have <sys/cdefs.h>.

Remove all <sys/cdefs.h> includes and write out __BEGIN_DECLS and
__END_DECLS.

Submitted by: Felix Janda
Ticket: #479

Fix build with clang: make variables static.

Include a supported option in the usage message printed by '''strings'''.

Ticket: #367