add the right flag to build with clang++ on Linux
add the right flag to build with clang++ on Linux

fix https://github.com/jamoma/JamomaCore/issues/380
thansk to @jcelerier

jamoma/JamomaCore,jamoma/JamomaCore,jamoma/JamomaCore,jamoma/JamomaCore,jamoma/JamomaCore,jamoma/JamomaCore,jamoma/JamomaCore