botan: Do not build on ARC

Not supported.

Signed-off-by: Rosen Penev <rosenp@gmail.com>

libs/botan/Makefile

@@ -41,7 +41,7 @@ define Package/libbotan
   CATEGORY:=Libraries
   TITLE+= (library)
   ABI_VERSION:=$(PKG_VERSION)-$(PKG_RELEASE)
-  DEPENDS:=+libstdcpp +libpthread
+  DEPENDS:=+libstdcpp +libpthread @!arc
 endef
 
 define Package/libbotan/description