Enabling OMPT sometimes requires setting OMP_TOOL_LIBRARIES

[jrmadsen]

It has been noted that some versions of OMPT in OpenMP v5 require:

export OMP_TOOL_LIBRARIES=libomnitrace-dl.so

In later versions, OpenMP will dlsym(RTLD_NEXT, ...) and look for ompt_start_tool.
To support older OMPT implementations omnitrace-dl should do this:

std::string _omni_omp_libs = "libomnitrace-dl.so";
const char* _omp_libs      = getenv("OMP_TOOL_LIBRARIES");
if(_omp_libs) 
    _omni_omp_libs = common::join(':', _omp_libs, "libomnitrace-dl.so");
setenv("OMP_TOOL_LIBRARIES", _omni_omp_libs.c_str(), 1);