gdb: Fix build breakage with GCC 4.1 and --disable-nls

Ref: https://sourceware.org/ml/gdb-patches/2016-09/msg00203.html

The std::{min,max} patch caused build failures when configuring GDB
with with --disable-nls and using GCC 4.1.

The reason is this bit in common/gdb_locale.h:

 #ifdef ENABLE_NLS
 ...
 #else
 # define gettext(Msgid) (Msgid)
 ...
 #endif

This causes problems if the <libintl.h> header is first included at
any point after "gdb_locale.h".

Specifically, the gettext&co declarations in libintl.h:

 extern char *gettext (__const char *__msgid)
      __THROW __attribute_format_arg__ (1);

end up broken after preprocessing:

 extern char *(__const char *__msgid)
      throw () __attribute__ ((__format_arg__ (1)));

After the std::min/std::max change to include <algorithm>, this now
happens with at least the GCC 4.1 copy of <algorithm>, which includes
<libintl.h> via <bits/stl_algobase.h>, <iosfwd>, and
<bits/c++locale.h>.

The fix is to simply remove the troublesome *gettext and *textdomain
macros, leaving only the _ and N_ ones.

gdb/ChangeLog:
2016-09-19  Pedro Alves  <palves@redhat.com>

	* common/gdb_locale.h [!ENABLE_NLS] (gettext, dgettext, dcgettext,
	textdomain, bindtextdomain): Delete macros.
	* main.c (captured_main) [!ENABLE_NLS]: Skip bintextdomain and
	textdomain calls.

gdb/main.c

@@ -501,8 +501,10 @@ captured_main (void *data)
 #if defined (HAVE_SETLOCALE)
   setlocale (LC_CTYPE, "");
 #endif
+#ifdef ENABLE_NLS
   bindtextdomain (PACKAGE, LOCALEDIR);
   textdomain (PACKAGE);
+#endif
 
   bfd_init ();
   notice_open_fds ();