libstdc++: Fix up to_chars ppc64le _Float128 overloads [PR107636]

As reported, I've misplaced __extension__ keywords in these cases
(wanted not to have them on the whole inlines because _Float128 is
completely standard now while __float128 is not, but before return
it is a syntax error.
I've verified on a short testcase that both g++ and clang++ accept
__extension__ after return keyword.

2022-11-12  Jakub Jelinek  <jakub@redhat.com>

	PR libstdc++/107636
	* include/std/charconv (to_chars): Fix up powerpc64le _Float128
	overload __extension__ placement.
diff --git a/libstdc++-v3/include/std/charconv b/libstdc++-v3/include/std/charconv
index acad865..c5ed6fa 100644
--- a/libstdc++-v3/include/std/charconv
+++ b/libstdc++-v3/include/std/charconv
@@ -892,23 +892,25 @@
   inline to_chars_result
   to_chars(char* __first, char* __last, _Float128 __value) noexcept
   {
-    __extension__
-    return to_chars(__first, __last, static_cast<__float128>(__value));
+    return __extension__ to_chars(__first, __last,
+				  static_cast<__float128>(__value));
   }
   inline to_chars_result
   to_chars(char* __first, char* __last, _Float128 __value,
 	   chars_format __fmt) noexcept
   {
-    __extension__
-    return to_chars(__first, __last, static_cast<__float128>(__value), __fmt);
+
+    return __extension__ to_chars(__first, __last,
+				  static_cast<__float128>(__value), __fmt);
   }
   inline to_chars_result
   to_chars(char* __first, char* __last, _Float128 __value,
 	   chars_format __fmt, int __precision) noexcept
   {
-    __extension__
-    return to_chars(__first, __last, static_cast<__float128>(__value), __fmt,
-		    __precision);
+
+    return __extension__ to_chars(__first, __last,
+				  static_cast<__float128>(__value), __fmt,
+				  __precision);
   }
 #else
   to_chars_result to_chars(char* __first, char* __last, _Float128 __value)