openntpd: needs NPTL

Openntpd in fact needs nptl threads, basic threads aren't enough. Fixes:
http://autobuild.buildroot.net/results/f4d/f4dd964231a5dbbc12a7237127fa9c45d6aa0d06/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/openntpd/Config.in

@@ -1,7 +1,7 @@
 config BR2_PACKAGE_OPENNTPD
 	bool "openntpd"
 	depends on BR2_INET_IPV6
-	depends on BR2_TOOLCHAIN_HAS_THREADS
+	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL
 	depends on BR2_USE_MMU # fork ()
 	depends on !BR2_PACKAGE_NTP # conflicting binaries
 	help
@@ -12,6 +12,6 @@ config BR2_PACKAGE_OPENNTPD
 
 	  http://www.openntpd.org/
 
-comment "openntpd needs a toolchain w/ threads, IPv6"
+comment "openntpd needs a toolchain w/ NPTL, IPv6"
 	depends on BR2_USE_MMU
-	depends on !BR2_INET_IPV6 || !BR2_TOOLCHAIN_HAS_THREADS
+	depends on !BR2_INET_IPV6 || !BR2_TOOLCHAIN_HAS_THREADS_NPTL