MFC r267436-267439:

- Replace malloc+memset with calloc.
- iconv_open(3): initialise ci_ilseq_invalid field of _citrus_iconv_shared
  struct after allocation with malloc.
- iconvlist(3): reduce a memory leak by copying strings only once.
- iconv(1):
  - Make invalids variable local to do_conv such that it prints the number
    of invalid characters of the current file instead of an accumulated
    value.
  - Make do_conv return an error when invalid characters have been found.
    Return EXIT_FAILURE from main if any file contained invalid characters.
    This matches the behaviour of GNU iconv.
  - Mark usage with __dead2 attribute.
  - Make the long_options array const.

Tested by:	Pavel Timofeev <timp87@gmail.com>
MFC r267441:

Don't install GSS-API headers when the GSSAPI option has been disabled.
Some ports assume GSS-API is supported when they find the headers.

PR:		189156
Submitted by:	Garrett Cooper <yanegomi@gmail.com>