sync features.h with GNU C library, fixes gcc 7.1 toolchain creation

include/features.h

@@ -55,6 +55,7 @@
    These are defined by this file and are used by the
    header files to decide what to declare or define:
 
+   __USE_ISOC11		Define ISO C11 things.
    __USE_ISOC99		Define ISO C99 things.
    __USE_ISOC95		Define ISO C90 AMD1 (C95) things.
    __USE_POSIX		Define IEEE Std 1003.1 things.
@@ -91,6 +92,7 @@
 
 
 /* Undefine everything, so we get a clean slate.  */
+#undef	__USE_ISOC11
 #undef	__USE_ISOC99
 #undef	__USE_ISOC95
 #undef	__USE_POSIX
@@ -151,6 +153,8 @@
 #ifdef _GNU_SOURCE
 # undef  _ISOC99_SOURCE
 # define _ISOC99_SOURCE	1
+# undef  _ISOC11_SOURCE
+# define _ISOC11_SOURCE	1
 # undef  _POSIX_SOURCE
 # define _POSIX_SOURCE	1
 # undef  _POSIX_C_SOURCE
@@ -223,11 +227,14 @@
 # define _SVID_SOURCE	1
 #endif
 
-/* This is to enable the ISO C99 extension.  Also recognize the old macro
+/* This is to enable the ISO C11 extension.  */
-   which was used prior to the standard acceptance.  This macro will
+#if (defined _ISOC11_SOURCE \
-   eventually go away and the features enabled by default once the ISO C99
+     || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 201112L))
-   standard is widely adopted.  */
+# define __USE_ISOC11	1
-#if (defined _ISOC99_SOURCE || defined _ISOC9X_SOURCE \
+#endif
+
+/* This is to enable the ISO C99 extension.  */
+#if (defined _ISOC99_SOURCE || defined _ISOC11_SOURCE \
      || (defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L))
 # define __USE_ISOC99	1
 #endif