Backport gettext fixes to get rid of warnings on macOS

Two fixes were committed recently to the gettext repo in order to make
gdb build warning-free on macOS.  This patch backports them both:

  - Make the format_arg attribute effective also in the case _INTL_REDIRECT_INLINE.
    113893dce80358a4ae0d9463ce73c5670c81cf0c
    http://git.savannah.gnu.org/cgit/gettext.git/commit/?id=113893dce80358a4ae0d9463ce73c5670c81cf0c

  - Enable the format_arg attribute also on clang on Mac OS X.
    bd6a52241c7c83c90e043ace2082a2508d273f55
    http://git.savannah.gnu.org/cgit/gettext.git/commit/?id=bd6a52241c7c83c90e043ace2082a2508d273f55

intl/ChangeLog:

	* libgnuintl.h (_INTL_MAY_RETURN_STRING_ARG, gettext, dgettext,
	dcgettext, ngettext, dngettext, dcngettext): Backport changes
	from upstream gettext.

intl/ChangeLog

@@ -1,3 +1,9 @@
+2018-08-02  Simon Marchi  <simon.marchi@ericsson.com>
+
+	* libgnuintl.h (_INTL_MAY_RETURN_STRING_ARG, gettext, dgettext,
+	dcgettext, ngettext, dngettext, dcngettext): Backport changes
+	from upstream gettext.
+
 2018-06-19  Simon Marchi  <simon.marchi@ericsson.com>
 
 	* configure.ac: Add AC_USE_SYSTEM_EXTENSIONS, remove AC_PREREQ.

intl/libgnuintl.h

@@ -115,7 +115,7 @@ extern "C" {
 /* _INTL_MAY_RETURN_STRING_ARG(n) declares that the given function may return
    its n-th argument literally.  This enables GCC to warn for example about
    printf (gettext ("foo %y")).  */
-#if __GNUC__ >= 3 && !(__APPLE_CC__ > 1 && defined __cplusplus)
+#if defined __GNUC__ && __GNUC__ >= 3 && !(defined __APPLE_CC__ && __APPLE_CC__ > 1 && !(defined __clang__ && __clang__ && __clang_major__ >= 3) && defined __cplusplus)
 # define _INTL_MAY_RETURN_STRING_ARG(n) __attribute__ ((__format_arg__ (n)))
 #else
 # define _INTL_MAY_RETURN_STRING_ARG(n)
@@ -127,7 +127,9 @@ extern "C" {
 #ifdef _INTL_REDIRECT_INLINE
 extern char *libintl_gettext (const char *__msgid)
        _INTL_MAY_RETURN_STRING_ARG (1);
-static inline char *gettext (const char *__msgid)
+static inline
+_INTL_MAY_RETURN_STRING_ARG (1)
+char *gettext (const char *__msgid)
 {
   return libintl_gettext (__msgid);
 }
@@ -145,7 +147,9 @@ extern char *gettext _INTL_PARAMS ((const char *__msgid))
 #ifdef _INTL_REDIRECT_INLINE
 extern char *libintl_dgettext (const char *__domainname, const char *__msgid)
        _INTL_MAY_RETURN_STRING_ARG (2);
-static inline char *dgettext (const char *__domainname, const char *__msgid)
+static inline
+_INTL_MAY_RETURN_STRING_ARG (2)
+char *dgettext (const char *__domainname, const char *__msgid)
 {
   return libintl_dgettext (__domainname, __msgid);
 }
@@ -165,8 +169,9 @@ extern char *dgettext _INTL_PARAMS ((const char *__domainname,
 extern char *libintl_dcgettext (const char *__domainname, const char *__msgid,
 				int __category)
        _INTL_MAY_RETURN_STRING_ARG (2);
-static inline char *dcgettext (const char *__domainname, const char *__msgid,
-			       int __category)
+static inline
+_INTL_MAY_RETURN_STRING_ARG (2)
+char *dcgettext (const char *__domainname, const char *__msgid, int __category)
 {
   return libintl_dcgettext (__domainname, __msgid, __category);
 }
@@ -188,8 +193,10 @@ extern char *dcgettext _INTL_PARAMS ((const char *__domainname,
 extern char *libintl_ngettext (const char *__msgid1, const char *__msgid2,
 			       unsigned long int __n)
        _INTL_MAY_RETURN_STRING_ARG (1) _INTL_MAY_RETURN_STRING_ARG (2);
-static inline char *ngettext (const char *__msgid1, const char *__msgid2,
-			      unsigned long int __n)
+static inline
+_INTL_MAY_RETURN_STRING_ARG (1) _INTL_MAY_RETURN_STRING_ARG (2)
+char *ngettext (const char *__msgid1, const char *__msgid2,
+		unsigned long int __n)
 {
   return libintl_ngettext (__msgid1, __msgid2, __n);
 }
@@ -210,8 +217,10 @@ extern char *ngettext _INTL_PARAMS ((const char *__msgid1,
 extern char *libintl_dngettext (const char *__domainname, const char *__msgid1,
 				const char *__msgid2, unsigned long int __n)
        _INTL_MAY_RETURN_STRING_ARG (2) _INTL_MAY_RETURN_STRING_ARG (3);
-static inline char *dngettext (const char *__domainname, const char *__msgid1,
-			       const char *__msgid2, unsigned long int __n)
+static inline
+_INTL_MAY_RETURN_STRING_ARG (2) _INTL_MAY_RETURN_STRING_ARG (3)
+char *dngettext (const char *__domainname, const char *__msgid1,
+		 const char *__msgid2, unsigned long int __n)
 {
   return libintl_dngettext (__domainname, __msgid1, __msgid2, __n);
 }
@@ -234,9 +243,11 @@ extern char *libintl_dcngettext (const char *__domainname,
 				 const char *__msgid1, const char *__msgid2,
 				 unsigned long int __n, int __category)
        _INTL_MAY_RETURN_STRING_ARG (2) _INTL_MAY_RETURN_STRING_ARG (3);
-static inline char *dcngettext (const char *__domainname,
-				const char *__msgid1, const char *__msgid2,
-				unsigned long int __n, int __category)
+static inline
+_INTL_MAY_RETURN_STRING_ARG (2) _INTL_MAY_RETURN_STRING_ARG (3)
+char *dcngettext (const char *__domainname,
+		  const char *__msgid1, const char *__msgid2,
+		  unsigned long int __n, int __category)
 {
   return libintl_dcngettext (__domainname, __msgid1, __msgid2, __n, __category);
 }