NVIDIA C++ compiler -cuda option triggers incompatible redefiniton of BOOST_COMPILER

[olupton]

Passing the -cuda option to nvc++ makes it define the __CUDACC__ macro, which in turn leads to a warning from Boost:

"config/include/boost/config/compiler/pgi.hpp", line 12: warning: incompatible redefinition of macro "BOOST_COMPILER" (declared at line 11 of "config/include/boost/config/compiler/nvcc.hpp")
  #define BOOST_COMPILER "PGI compiler version " BOOST_STRINGIZE(BOOST_COMPILER_VERSION)
          ^

(tested with today's develop, c11afa5, and the 1.78 release).

nvc++ also defines macros such as __PGI and __NVCOMPILER.