package/trousers: fix build with libressl >= 2.7.0

Fix the following build failure with libressl >= 2.7.0:

crypto/openssl/rsa.c:43:1: error: static declaration of 'RSA_set0_key' follows non-static declaration
   43 | RSA_set0_key(RSA *r, BIGNUM *n, BIGNUM *e, BIGNUM *d)
      | ^~~~~~~~~~~~

Fixes:
 - http://autobuild.buildroot.org/results/607131255453da2dc0dab20a24264b3e74001525

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/trousers/0003-Fix-build-with-LibreSSL-2-7.patch

@@ -0,0 +1,24 @@
+Fix build with LibreSSL 2.7 
+
+LibreSSL 2.7 implemented OpenSSL 1.1 API
+
+See also: https://reviews.freebsd.org/D14849#change-KhYbRXBMIBod
+
+Cheers,
+Bernard Spil (brnrd@FreeBSD.org)
+
+[Retrieved (and backported) from:
+https://sourceforge.net/p/trousers/bugs/234]
+Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
+
+--- ./src/trspi/crypto/openssl/rsa.c.orig	2016-11-23 12:26:19 UTC
++++ ./src/trspi/crypto/openssl/rsa.c
+@@ -38,7 +38,7 @@
+ #define DEBUG_print_openssl_errors()
+ #endif
+ 
+-#if (OPENSSL_VERSION_NUMBER < 0x10100001L) || defined(LIBRESSL_VERSION_NUMBER)
++#if (OPENSSL_VERSION_NUMBER < 0x10100001L) || (defined(LIBRESSL_VERSION_NUMBER) && LIBRESSL_VERSION_NUMBER < 0x20700000L)
+ static int
+ RSA_set0_key(RSA *r, BIGNUM *n, BIGNUM *e, BIGNUM *d)
+ {