erlang: needs thread support

Fixes:

  http://autobuild.buildroot.org/results/1f3/1f313aee75328c27e260c55dbf7caa5d3d6a07d3/
  http://autobuild.buildroot.org/results/2f2/2f213d8cf6f828a68a2f36bb95564b8db043e7a2/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/erlang/Config.in

@@ -1,6 +1,10 @@
+comment "erlang needs a toolchain w/ threads"
+	depends on !BR2_TOOLCHAIN_HAS_THREADS
+
 config BR2_PACKAGE_ERLANG
 	bool "erlang"
 	depends on BR2_USE_MMU # fork()
+	depends on BR2_TOOLCHAIN_HAS_THREADS
 	help
 	  Erlang is a programming language used to build massively scalable
 	  soft real-time systems with requirements on high availability.