Turn off -Wnon-virtual-dtor explicitly

adb has been built without -Wnon-virtual-dtor because Soong doesn't turn
the flag for the host targets, and the flag can't coexist with
-Wexit-time-destructors.

However, the new host target linux_bionic_arm64 turns the flag on,
because it inherits most of the cflags from the device config.
That is forcing us to implement the virtual destructor, which isn't
possible due to -Wexit-time-destructors.

Solving the issue by explicitly turning -Wnon-virtual-dtor off so that
it is disabled also for the linux_bionic_arm64 target.

Bug: 159685774
Test: HOST_CROSS_OS=linux_bionic HOST_CROSS_ARCH=arm64 m \
out/soong/host/linux_bionic-arm64/bin/adb
Test: run the adb on an ARM emulator

Change-Id: I655b340e4f199a3a75b7df7cc3fe18832e26a7ae