package/libressl: depend on threads

If the toolchain does not have threads (e.g. br-arm-full-nothread),
compilation fails:

In file included from /home/fail/br-test-pkg/br-arm-full-nothread/build/libressl-3.3.3/crypto/cryptlib.c:117:
/home/fail/br-test-pkg/br-arm-full-nothread/build/libressl-3.3.3/crypto/../include/compat/pthread.h:114:15: fatal error: pthread.h: No such file or directory
  114 | #include_next <pthread.h>
      |               ^~~~~~~~~~~
compilation terminated.

Signed-off-by: Nicolas Cavallari <nicolas.cavallari@green-communications.fr>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
(cherry picked from commit da8f069d745de73fb5810c21b2896ff173fa6090)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/openssl/Config.in

@@ -33,6 +33,7 @@ source "package/libopenssl/Config.in"
 config BR2_PACKAGE_LIBRESSL
 	bool "libressl"
 	depends on !BR2_PACKAGE_OPENSSL_FORCE_LIBOPENSSL
+	depends on BR2_TOOLCHAIN_HAS_THREADS
 	# uClibc on noMMU doesn't provide __register_atfork()
 	depends on !(BR2_TOOLCHAIN_USES_UCLIBC && !BR2_USE_MMU)
 	help