radeonsi: for the tess barrier, only use emit_waitcnt on SI and LLVM 3.9+
radeonsi: for the tess barrier, only use emit_waitcnt on SI and LLVM 3.9+

Cc: 17.0 13.0 <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>
Reviewed-by: Edward O'Callaghan <b035da0d7e151e09fe2005f3a7bc526beb9b3245@folklore1984.net>
Reviewed-by: Nicolai Hähnle <0d0be6cf5ad662651be2dc5dfd44aa2b09d4c1cc@amd.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler