Add -ldl for new stlport

The new stlport in NDK r8d+ supports exception support via gabi++.
The new gabi++ depends on dlopen, etc, meaning that we need to add -ldl
for project links stlport with "-nostdlib -Wl,--no-undefined"
(ie. all *.so in Android)

Change-Id: I7321a075d2852a6a72f82f40bb24d64ec211cf39