cudatoolkit: Fix building dependent packages

- Set a cmake flag to allow cmake to find CUDA automatically.

- Pass -D_FORCE_INLINES to work around

    /nix/store/8sl4jfs3nq0pkq4gg655s3axrxdx7z29-glibc-2.24-dev/include/string.h: In function 'void* __mempcpy_inline(void*, const void*, size_t)':
    /nix/store/8sl4jfs3nq0pkq4gg655s3axrxdx7z29-glibc-2.24-dev/include/string.h:650:42: error: 'memcpy' was not declared in this scope

  https://github.com/BVLC/caffe/issues/4046

This fixes OpenSubdiv and Blender.