Fix compilation error on hip-hcc+clang , hip-vdi+clang
Enabled hipExtLaunchMultiKernelMultiDevice test on hip-vdi path
hipExtLaunchMultiKernelMultiDevice common declaration for all paths
Change-Id: I76031840614fce8e12a8e845548fa43a389a741a
[ROCm/hip commit: 6a5d04209c]