par: fix static build

This change causes rebuild of both glibc and musl dynamic variants, but
no cascade rebuilds.

pkgs/tools/text/par/default.nix

@@ -18,7 +18,12 @@ stdenv.mkDerivation {
     })
   ];
 
-  buildPhase = ''make -f protoMakefile'';
+  makefile = "protoMakefile";
+  preBuild = ''
+    makeFlagsArray=+( CC="${stdenv.cc.targetPrefix}cc -c" \
+                      LINK1=${stdenv.cc.targetPrefix}cc   \
+                    )
+  '';
 
   installPhase = ''
     mkdir -p $out/bin