m4, help2man: Update from gnulib

m4, help2man: Update from gnulib

* gettext-runtime/m4/codeset.m4: Update copyright year.
* gettext-runtime/m4/gettext.m4: Likewise.
* gettext-runtime/m4/iconv.m4: Likewise.
* gettext-runtime/m4/intl.m4: Likewise.
* gettext-runtime/m4/intldir.m4: Likewise.
* gettext-runtime/m4/intlmacosx.m4: Likewise.
* gettext-runtime/m4/lcmessage.m4: Likewise.
* gettext-runtime/m4/nls.m4: Likewise.
* gettext-runtime/m4/po.m4: Likewise.
* gettext-runtime/m4/extern-inline.m4: Likewise.  Port the following
change:
  2015-04-29  Paul Eggert  <eggert@cs.ucla.edu>
    extern-inline: no need for workaround in GCC 5.1
    * doc/extern-inline.texi (extern inline):
    * m4/extern-inline.m4 (gl_EXTERN_INLINE):
    GCC bugs 54113 and 63877 are fixed in GCC 5.1, so don't work
    around these bugs in GCC 5.1 and later.  Maybe in a decade or
    two we can remove these workarounds.
* gettext-tools/man/help2man: Update copyright year.