vndk-def: Fix unittests with rpath

This commit adds -Wl,--disable-new-dtags to the unit tests that expect
DT_RPATH entries.  The latest toolchain defaults to --enable-new-dtags
now, thus we have to specify -Wl,--disable-new-dtags explicitly.

Test: ./tests/test_elfdump.py
Change-Id: I64c1210a8f04415b0b836db480463c172bcf0d71