anchor.diff:  
     buildInputs = [ gmp mpfr mpc libelf ]
       ++ (optional (ppl != null) ppl)
  -    ++ (optional (cloogppl != null) cloogppl)
       ++ (optional (cloog != null) cloog)
       ++ (optional (zlib != null) zlib)
       ++ (optionals langJava [ boehmgc zip unzip ])
  
positive.code: , perl ? null # optional, for texi2pod (then pod2man); required for Java
  , gmp, mpfr, mpc, gettext, which
  , libelf                      # optional, for link-time optimizations (LTO)
  , ppl ? null, cloogppl ? null, cloog ? null # optional, for the Graphite optimization framework. Cannot pass both cloog and cloogppl
  , zlib ? null, boehmgc ? null
  , zip ? null, unzip ? null, pkgconfig ? null, gtk ? null, libart_lgpl ? null
  , libX11 ? null, libXt ? null, libSM ? null, libICE ? null, libXtst ? null
  
negative.code:       ${if enableMultilib then "" else "--disable-multilib"}
        ${if enableShared then "" else "--disable-shared"}
        ${if ppl != null then "--with-ppl=${ppl.hostDrv}" else ""}
        ${if cloog != null then "--with-cloog=${cloog.hostDrv} --enable-cloog-backend=isl" else ""}
        ${if langJava then "--with-ecj-jar=${javaEcj.hostDrv}" else ""}
        ${if javaAwtGtk then "--enable-java-awt=gtk" else ""}
  