Fix volantis boot.

NVIDIA binary blobs are assuming that __cache_clear, _Unwind_Backtrace,
and _Unwind_GetIP are all in some library that they link, but now we've
cleaned up this leakage, they're no longer getting it. Deliberately leak
the symbols from libc.so until we get new blobs.

Bug: http://b/20065774
Change-Id: I92ef07b2bce8d1ad719bf40dab41d745cd6904d4