It doesn't seem to work (any longer in 10.12) to pass
DYLD_LIBRARY_PATH in the environment to the process to be run under
lldb. We need to make lldb execute an explicit 'settings set
target.env-vars' command. Use a temporary file to pass that command.

I could not figure out where to call the gb_CppunitTest_POSTGDBTRACE
macro I define, to remove the temporary file, sorry. Help appreciated.

Change-Id: I46bd05f14623639e6ce10112b92ef497cdbb0755