Further simplify configure-time locale testing

* configure.ac (gl_STDLIB_H): Replace this, not gt_LOCALE_FR_UTF8,
as this lets us also omit MB_CUR_MAX checking that will never be
executed, and also lets us remove testing for ecvt, fcvt, gcvt
that Emacs doesn’t need.
(AC_C_RESTRICT): Invoke explicitly, as Emacs uses ‘restrict’
directly.  Also, simplifies the replacement for gl_STDLIB_H, which
would otherwise need to AC_REQUIRE AC_C_RESTRICT.
* lib/gnulib.mk.in: Regenerate via admin/merge-gnulib.

configure.ac

@@ -902,9 +902,9 @@ AC_DEFUN([gt_TYPE_WINT_T],
   [GNULIBHEADERS_OVERRIDE_WINT_T=0
    AC_SUBST([GNULIBHEADERS_OVERRIDE_WINT_T])])
 # Emacs does not need precise checks for the Solaris 10 MB_CUR_MAX bug.
-AC_DEFUN([gt_LOCALE_FR_UTF8],
-  [LOCALE_FR_UTF8=none
-   AC_SUBST([LOCALE_FR_UTF8])])
+AC_DEFUN_ONCE([gl_STDLIB_H],
+  [AC_REQUIRE([gl_STDLIB_H_DEFAULTS])
+   gl_NEXT_HEADERS([stdlib.h])])
 
 # Initialize gnulib right after choosing the compiler.
 dnl Amongst other things, this sets AR and ARFLAGS.
@@ -6305,6 +6305,7 @@ if test "$emacs_cv_struct_alignment" = yes; then
      structure to an N-byte boundary.])
 fi
 
+AC_C_RESTRICT
 AC_C_TYPEOF
 
 AC_CACHE_CHECK([for statement expressions],

lib/gnulib.mk.in

@@ -961,7 +961,6 @@ LIB_WSOCK32 = @LIB_WSOCK32@
 LIB_XATTR = @LIB_XATTR@
 LIMITS_H = @LIMITS_H@
 LN_S_FILEONLY = @LN_S_FILEONLY@
-LOCALE_FR_UTF8 = @LOCALE_FR_UTF8@
 LTLIBGMP = @LTLIBGMP@
 LTLIBINTL = @LTLIBINTL@
 LTLIBOBJS = @LTLIBOBJS@