Fix bsls_nullptr test driver to pass in C++11 on more compilers
Fix bsls_nullptr test driver to pass in C++11 on more compilers

While not testing all possible levels of gcc and Clang compilers,
this patch should produce clean test results on all compilers that
are tested as part of the one-shot and nightly regressions.

che2/bde,bloomberg/bde,bloomberg/bde,che2/bde,che2/bde,bloomberg/bde,che2/bde,bloomberg/bde,bloomberg/bde