Fix clang warnings.

[scott-snyder]

Unused variables.

BEGINRELEASENOTES

• Fix some unused variable warnings seen when compiling with clang.
  ENDRELEASENOTES

[scott-snyder]

In the tests, we were getting the warnings because the variable in question was used only in assert(), which was being suppressed. Rather then suppress the unused variable warning, instead undefine NDEBUG for these sources so that the assertions are always there.

[tmadlener]

Thanks a lot.