Increases size of llvm@6 by 2.5MiB (2.5%), but saves building specialized
llvm's with rtti enabled for packages that require RTTI when linking with the
llvm libraries.
* gnu/packages/llvm.scm (llvm-3.8-with-rtti): Remove variable.
(llvm)[arguments]: Add '-DLLVM_REQUIRES_RTTI=1' to #:configure-flags.
* gnu/packages/audio.scm (faust-2)[native-inputs]:
'llvm-3.8-with-rtti' -> 'llvm-3.8'.
* gnu/packages/audio.scm (clalsadrv, jack-2, libsbsms, zita-convolver)
(zita-resampler, zita-alsa-pcmi, gsm, cava): Return #t from all phases.
(ladspa): Use 'modify-phases'. Return #t from all phases.
* gnu/packages/audio.scm (faust-2): Update to 2.5.23.
[native-inputs]: Replace llvm-with-rtti with llvm-3.8-with-rtti.
* gnu/packages/llvm.scm (llvm-with-rtti): Rename this variable...
(llvm-3.8-with-rtti): ...to this variable; inherit from llvm-3.8.