csound: fix build (pthread not found) by adding stdenv.cc.libc.out/lib to -L. No idea why this is not default enough specifically when cmake is used

+2
+2
pkgs/applications/audio/csound/default.nix
··· 23 23 24 24 buildInputs = [ cmake libsndfile flex bison alsaLib libpulseaudio tcltk ]; 25 25 26 + NIX_LDFLAGS="-L${stdenv.cc.libc.out}/lib"; 27 + 26 28 meta = { 27 29 description = "sound design, audio synthesis, and signal processing system, providing facilities for music composition and performance on all major operating systems and platforms"; 28 30 homepage = http://www.csounds.com/;