crash-u.cc: add a simple way to blacklist systems because backtrace() is unavailable

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

Created by  Steven Noonan  on October 21, 2009
DW6NUKWCSXAFD76T7EGR6F2XRBC3WMLRBWIX5HKPGEPFLSCHXDGAC
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