Fixed CMake 2.8.12+ CUDA dylib bugs and warnings on OS X

This patch fixes up a number of minor compilation issues
with CUDA on OS X. The __STRICT_ANSI__ define has been
added to make CUDA work with gcc version 4.8 and 4.9,
a dummy variable has been added to the dummy c++ gpu utils
file to avoid warnings about empty objects, and we now
properly handle both RPATH (newer CMake) and INSTALL_NAME_DIR
(older CMake) without warnings. CMake-2.8.12 introduced
a bug that caused Gromacs executables to be malformed since
the rpath to the CUDA libraries was added twice. This is
caused by fairly deep internal changes in CMake, but it has
been worked around by removing the rpath (which FindCUDA.cmake
only adds on OS X) manually for CMake>2.8.11.

Fixes #1471.

Change-Id: I8b01204dc07678bc305821162f20db65e0e7b88d