[DynInst_API:] dyninst and nullptr don't build with g++ 4.4

["Mark W. Krentel" <krentel@xxxxxxxx>]

The latest Dyninst master fails to build with g++ 4.4.  It builds ok
with g++ 4.8, but not 4.4.

The problem is that dataflowAPI/src/stackanalysis.C now uses nullptr
which is not supported in g++ 4.4.

[ 55%] Building CXX object 
parseAPI/CMakeFiles/parseAPI.dir/__/dataflowAPI/src/stackanalysis.C.o
/home/krentel/newelf/externals/BUILD/symtabAPI/dyninst/dataflowAPI/src/stackanalysis.C:64:
error: 'nullptr' was not declared in this scope
/home/krentel/newelf/externals/BUILD/symtabAPI/dyninst/dataflowAPI/src/stackanalysis.C:66:
error: 'nullptr' was not declared in this scope
/home/krentel/newelf/externals/BUILD/symtabAPI/dyninst/dataflowAPI/src/stackanalysis.C:68:
error: 'nullptr' was not declared in this scope
/home/krentel/newelf/externals/BUILD/symtabAPI/dyninst/dataflowAPI/src/stackanalysis.C:70:
error: 'nullptr' was not declared in this scope
make[5]: *** 
[parseAPI/CMakeFiles/parseAPI.dir/__/dataflowAPI/src/stackanalysis.C.o] 
Error 1
Looking at the table of C++11 features in GCC, it seems that nullptr
is not supported until 4.6.

   https://gcc.gnu.org/projects/cxx-status.html

So, I'm not sure how you want to handle this.  But using nullptr means
that you can't build Dyninst from source on RH 6.x, at least not
without installing a whole new compiler.

--Mark