package/opentracing-cpp: needs threads

opentracing-cpp uses std::mutex since 1.3.0.

Fixes: http://autobuild.buildroot.net/results/121a9f2aacf9e7b1f5d0b3f2c55bc1da36c7cfb6/

Signed-off-by: Thomas De Schampheleire <thomas.de_schampheleire@nokia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/opentracing-cpp/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_OPENTRACING_CPP
 	bool "opentracing-cpp"
 	depends on BR2_INSTALL_LIBSTDCPP
+	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_8 # C++11
 	depends on !BR2_TOOLCHAIN_HAS_GCC_BUG_64735 # exception_ptr
 	help
@@ -8,8 +9,8 @@ config BR2_PACKAGE_OPENTRACING_CPP
 
 	  http://opentracing.io
 
-comment "opentracing-cpp needs a toolchain w/ C++, gcc >= 4.8"
-	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
+comment "opentracing-cpp needs a toolchain w/ C++, threads, gcc >= 4.8"
+	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_HAS_THREADS || !BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
 
 comment "opentracing-cpp needs exception_ptr"
 	depends on BR2_TOOLCHAIN_HAS_GCC_BUG_64735