Add missing log.o dependency to linux_client_unittest target.

Add missing log.o dependency to linux_client_unittest target.

r945 introduced src/client/linux/log/log.c, which is used in
exception_handler.cc, and thus should be added as a dependency
in the linux_client_unittest target.

TEST=Compile and run unit tests on Linux.
Committed: https://code.google.com/p/google-breakpad/source/detail?r=946

[Ben Chan]

Fix compilation of unit tests on Linux

[Mark Mentovai]

LGTM