fix cmake for IDE creating subdir for exe

Under Visual Studio (at least), the exe are located in subdirectory of the binary directory (one for each build config: debug, release etc.). This does not work well with our copying the sources for CUDA kernels to the binary dir: the runtime directory is the subdirectory and thus the kernels are not detected (being in the parent dir). Explicitly looking for them in parent dir is not sufficient due to runtime dependendant pathes.

Workaround: explicitly forcing all runtime execution (for each config) to be in the binary dir where the src are moved.

A alternative way would be to create a binary directory for each config and copying the srcs in each of them...