fallback _GL_ATTRIBUTE_* definitions in intl.m4

[Daiki Ueno]

Hi,

There are growing number of uses of _GL_ATTRIBUTE_* in Gnulib source
files, which are also shared with libintl.  Since libintl can be copied
into non-Gnulib projects, we have to add fallback definitions to the
libintl source.  However, this might cause divergence between Gnulib and
gettext in the future.

So, in the gettext git, I added a new M4 macro gt_GL_ATTRIBUTE, which
copies necessary C macros from gnulib-common.m4:

  AC_DEFUN([AM_INTL_SUBDIR],
  [...
    AC_REQUIRE([gt_GL_ATTRIBUTE])dnl
  ])

  AC_DEFUN([gt_GL_ATTRIBUTE], [
    m4_ifndef([gl_[]COMMON],
      AH_VERBATIM([gt_gl_attribute],
  [#ifndef _GL_ATTRIBUTE_PURE
   #define _GL_ATTRIBUTE_PURE ...

Actual commit in gettext:
http://git.savannah.gnu.org/cgit/gettext.git/commit/?h=maint&id=0f8e2cca

Does this look OK?  I'd like someone to double-check if it does not
break anything.  Or, are there any better ideas?

Regards,
-- 
Daiki Ueno