gnutls: needs argp-standalone for musl/uclibc

It's required for crywrap (tools), fixes:
http://autobuild.buildroot.net/results/2d9/2d98fced7ff7c3b5c39a97eb1c8db7dd651fa86c/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gnutls/Config.in

@@ -14,6 +14,8 @@ if BR2_PACKAGE_GNUTLS
 
 config BR2_PACKAGE_GNUTLS_TOOLS
 	bool "install tools"
+	select BR2_PACKAGE_ARGP_STANDALONE \
+		if BR2_TOOLCHAIN_USES_UCLIBC || BR2_TOOLCHAIN_USES_MUSL
 	help
 	  Install GnuTLS command line tools for various cryptographic tasks.
 

package/gnutls/gnutls.mk

@@ -44,6 +44,12 @@ ifeq ($(BR2_PACKAGE_GNUTLS_TOOLS),)
 GNUTLS_CONF_OPTS += --disable-crywrap
 endif
 
+# Prerequisite for crywrap
+ifeq ($(BR2_PACKAGE_ARGP_STANDALONE),y)
+GNUTLS_CONF_ENV += LIBS="-largp"
+GNUTLS_DEPENDENCIES += argp-standalone
+endif
+
 # libidn support for nommu must exclude the crywrap wrapper (uses fork)
 GNUTLS_CONF_OPTS += $(if $(BR2_USE_MMU),,--disable-crywrap)