We simply don't emit unwind tables, which are not needed anyways since
we're compiling without exceptions. the combined saving for all four
targets we support is about 120K.
This seems to improve .aar's compression, for a total gain of 152 KiB.
We also disable stack-protector in the jni code, since it wasn't
enabled in libfilament.a anyways. However, we now compile all debug
builds with -fstack-protector
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