gnutls: Fix build with uclibc-ng

Recent gnutls update introduced "gnulib module fopen" (gl/fopen.c) which
tries to get fopen() declaration from stdio.h by defining __need_FILE
before including the header. While this seems unnecessary for the
purpose (alegedly __need_FILE is used by headers including stdio.h to
get the FILE declaration while avoiding namespace pollution),
uClibc-ng's stdio.h behaves unexpected if __need_FILE is defined:

1) features.h is not included, therefore __BEGIN_NAMESPACE_STD (and
   likely more) is not known later on
2) it declares *only* FILE, nothing else

To avoid these problems, don't define __need_FILE in gnutls and pray
this works with other libc's as well. Actually one should fix uClibc-ng
instead.

Signed-off-by: Phil Sutter <phil@nwl.cc>

package/gnutls/patches/0001-uclibc.patch

@@ -0,0 +1,32 @@
+diff -ur gnutls-3.6.16.orig/gl/fopen.c gnutls-3.6.16/gl/fopen.c
+--- gnutls-3.6.16.orig/gl/fopen.c	2021-05-24 10:04:41.000000000 +0200
++++ gnutls-3.6.16/gl/fopen.c	2021-10-29 14:28:33.850290352 +0200
+@@ -19,12 +19,10 @@
+ /* If the user's config.h happens to include <stdio.h>, let it include only
+    the system's <stdio.h> here, so that orig_fopen doesn't recurse to
+    rpl_fopen.  */
+-#define __need_FILE
+ #include <config.h>
+ 
+ /* Get the original definition of fopen.  It might be defined as a macro.  */
+ #include <stdio.h>
+-#undef __need_FILE
+ 
+ static FILE *
+ orig_fopen (const char *filename, const char *mode)
+diff -ur gnutls-3.6.16.orig/src/gl/fopen.c gnutls-3.6.16/src/gl/fopen.c
+--- gnutls-3.6.16.orig/src/gl/fopen.c	2021-05-24 10:05:13.000000000 +0200
++++ gnutls-3.6.16/src/gl/fopen.c	2021-10-29 14:28:41.435290892 +0200
+@@ -19,12 +19,10 @@
+ /* If the user's config.h happens to include <stdio.h>, let it include only
+    the system's <stdio.h> here, so that orig_fopen doesn't recurse to
+    rpl_fopen.  */
+-#define __need_FILE
+ #include <config.h>
+ 
+ /* Get the original definition of fopen.  It might be defined as a macro.  */
+ #include <stdio.h>
+-#undef __need_FILE
+ 
+ static FILE *
+ orig_fopen (const char *filename, const char *mode)