component/nettle: Provide openssl infromation

Nettle has hard dependency on openssl, and --disable-openssl is only
disabling optional feature of it.

component/nettle/buildout.cfg

@@ -18,5 +18,5 @@ configure-option =
   --disable-documentation
 environment =
   PATH=${m4:location}/bin:${patch:location}/bin:%(PATH)s
-  CPPFLAGS=-I${gmp:location}/include
-  LDFLAGS=-L${gmp:location}/lib -Wl,-rpath=${gmp:location}/lib -Wl,-rpath=@@LOCATION@@/lib
+  CPPFLAGS=-I${gmp:location}/include -I${openssl:location}/include
+  LDFLAGS=-L${gmp:location}/lib -Wl,-rpath=${gmp:location}/lib -Wl,-rpath=@@LOCATION@@/lib -L${openssl:location}/lib -Wl,-rpath=${openssl:location}/lib