Do the right thing if scons is run under scan-build.

scan-build is a wrapper script that applies the Clang Static Analyzer to
your code during compilation.  I'm please to report that the Analyzer's
default checkers find nothing to complain about in our code as of now.
Good!
Merge pull request #6 from AlisaMaas/clang-analyzer

Support building under the Clang Static Analyzer