Forward install RPATH setting to runtimes

[vedranmiletic]

No description provided.

[vedranmiletic]

@petrhosek Could you please take a look? I don't have write access to add a reviewer.

[petrhosek]

This would use the same RPATH for all targets and I'm not sure if that's desirable.

To set RPATH for individual targets, you can use:

set(RUNTIMES_${TARGET_TRIPLE}_CMAKE_INSTALL_RPATH "${INSTALL_RPATH}" CACHE STRING "")
set(RUNTIMES_${TARGET_TRIPLE}_CMAKE_BUILD_WITH_INSTALL_RPATH ON CACHE BOOL "")