ngettext support

ngettext support

binutils has lacked proper pluralization of output messages for a long
time, for example, readelf will display information about a section
that "contains 1 entries" or "There are 1 section headers".  Fixing
this properly requires us to use ngettext, because other languages
have different rules to English.

This patch defines macros for ngettext and friends to handle builds
with --disable-nls, and tidies the existing nls support.  I've
redefined gettext rather than just defining "_" as dgettext in bfd and
opcodes in case someone wants to use gettext there (which might
conceivably happen with generated code).

bfd/
	* sysdep.h: Formatting, comment fixes.
	(gettext, ngettext): Redefine when ENABLE_NLS.
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.
	(_): Define using gettext.
	(textdomain, bindtextdomain): Use safer "do nothing".
	* hosts/alphavms.h (textdomain, bindtextdomain): Likewise.
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.
opcodes/
	* opintl.h: Formatting, comment fixes.
	(gettext, ngettext): Redefine when ENABLE_NLS.
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.
	(_): Define using gettext.
	(textdomain, bindtextdomain): Use safer "do nothing".
binutils/
	* sysdep.h (textdomain, bindtextdomain): Use safer "do nothing".
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.
gas/
	* asintl.h (textdomain, bindtextdomain): Use safer "do nothing".
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.
gold/
	* system.h (textdomain, bindtextdomain): Use safer "do nothing".
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.
ld/
	* ld.h (textdomain, bindtextdomain): Use safer "do nothing".
	(ngettext, dngettext, dcngettext): Define when !ENABLE_NLS.