package/nodejs: disable for static build

nodejs requires dlopen(), etc.

Fixes:
http://autobuild.buildroot.net/results/87d/87dab0186abd7b2737a56b2f939f3aba294e8772/
http://autobuild.buildroot.net/results/be1/be1010a3a31642d49ec3a118858c77fed2f762b8/



[Thomas: add comment explaining that we could support static linking
on ARMv5, but we don't do it since it's too much of a corner case.]

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>