package/minisign: needs threads

Fix the following build failure raised since the addition of the package
in commit d90ac63d9b3448a239bb9aa8030326699a3fdc3d:
  Could NOT find Threads (missing: Threads_FOUND)

Fixes:
 - http://autobuild.buildroot.org/results/8d63a88291de945661a936d2437917a3428de276

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/minisign/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_MINISIGN
 	bool "minisign"
+	depends on BR2_TOOLCHAIN_HAS_THREADS
 	select BR2_PACKAGE_LIBSODIUM
 	select BR2_PACKAGE_LIBSODIUM_FULL
 	help
@@ -7,3 +8,6 @@ config BR2_PACKAGE_MINISIGN
 	  signatures.
 
 	  https://github.com/jedisct1/minisign
+
+comment "minisign needs a toolchain w/ threads"
+	depends on !BR2_TOOLCHAIN_HAS_THREADS