lua: remove unsupported flags for llvm
lua: remove unsupported flags for llvm

Prevents error:

  clang: error: unknown argument: '-fstack-usage'
  clang: error: unknown argument: '-fconserve-stack'

The flags are here to print debug information and try to optimize stack but are
not required.

authmillenon/RIOT,authmillenon/RIOT,aeneby/RIOT,OTAkeys/RIOT,toonst/RIOT,toonst/RIOT,A-Paul/RIOT,x3ro/RIOT,jasonatran/RIOT,rfuentess/RIOT,smlng/RIOT,kYc0o/RIOT,ant9000/RIOT,avmelnikoff/RIOT,biboc/RIOT,kYc0o/RIOT,kbumsik/RIOT,kYc0o/RIOT,mtausig/RIOT,biboc/RIOT,cladmi/RIOT,mtausig/RIOT,josephnoir/RIOT,OTAkeys/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,basilfx/RIOT,ant9000/RIOT,mfrey/RIOT,biboc/RIOT,OTAkeys/RIOT,yogo1212/RIOT,x3ro/RIOT,kaspar030/RIOT,gebart/RIOT,josephnoir/RIOT,ant9000/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,cladmi/RIOT,OlegHahm/RIOT,rfuentess/RIOT,authmillenon/RIOT,kbumsik/RIOT,x3ro/RIOT,aeneby/RIOT,BytesGalore/RIOT,smlng/RIOT,jasonatran/RIOT,authmillenon/RIOT,gebart/RIOT,OlegHahm/RIOT,OlegHahm/RIOT,kbumsik/RIOT,kYc0o/RIOT,rfuentess/RIOT,ant9000/RIOT,x3ro/RIOT,smlng/RIOT,basilfx/RIOT,A-Paul/RIOT,lazytech-org/RIOT,OlegHahm/RIOT,lazytech-org/RIOT,aeneby/RIOT,yogo1212/RIOT,rfuentess/RIOT,yogo1212/RIOT,kaspar030/RIOT,biboc/RIOT,mfrey/RIOT,mfrey/RIOT,mtausig/RIOT,miri64/RIOT,miri64/RIOT,basilfx/RIOT,smlng/RIOT,biboc/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,cladmi/RIOT,BytesGalore/RIOT,RIOT-OS/RIOT,mtausig/RIOT,lazytech-org/RIOT,x3ro/RIOT,OTAkeys/RIOT,smlng/RIOT,authmillenon/RIOT,kbumsik/RIOT,rfuentess/RIOT,gebart/RIOT,kaspar030/RIOT,avmelnikoff/RIOT,kYc0o/RIOT,A-Paul/RIOT,toonst/RIOT,kbumsik/RIOT,yogo1212/RIOT,authmillenon/RIOT,miri64/RIOT,kaspar030/RIOT,aeneby/RIOT,mfrey/RIOT,A-Paul/RIOT,BytesGalore/RIOT,josephnoir/RIOT,BytesGalore/RIOT,aeneby/RIOT,gebart/RIOT,ant9000/RIOT,yogo1212/RIOT,avmelnikoff/RIOT,OTAkeys/RIOT,lazytech-org/RIOT,toonst/RIOT,kaspar030/RIOT,basilfx/RIOT,yogo1212/RIOT,basilfx/RIOT,BytesGalore/RIOT,cladmi/RIOT,jasonatran/RIOT,gebart/RIOT,A-Paul/RIOT,RIOT-OS/RIOT,toonst/RIOT,cladmi/RIOT,avmelnikoff/RIOT,avmelnikoff/RIOT,mfrey/RIOT,miri64/RIOT,miri64/RIOT,jasonatran/RIOT,lazytech-org/RIOT,mtausig/RIOT