[OpenMP] Disable libomptarget profiling by default if built via the "runtimes" setup

In the "runtimes" setup, the runtime (e.g. OpenMP) can be built for
a target entirely different from the current host build (where LLVM
and Clang are built). If profiling is enabled, libomptarget links
against LLVMSupport (which only has been built for the host).

Thus, don't enable profiling by default in this setup.

This should allow relanding D113253.

Differential Revision: https://reviews.llvm.org/D114083