set target for darwin binary compat in skarnet.org packages

skalibs:
execline:
s6-dns:
s6-networking:
s6-portable-utils:
s6-rc:
s6:

The above software uses the target triplet from `cc -dumpmachine` as a
binary compatibility check. However, on darwin, the output includes the
darwin version number, which leads to build failures against a binary
skalibs package built a different version of darwin than the current
system.

Explicitly setting target ensures code can be compiled against a skalibs
binary built on a different version of darwin.

See http://www.skarnet.org/cgi-bin/archive.cgi?1:mss:623:heiodchokfjdkonfhdph

pkgs/development/libraries/skalibs/default.nix

@@ -23,7 +23,14 @@ in stdenv.mkDerivation rec {
     "--libdir=\${prefix}/lib"
     "--includedir=\${prefix}/include"
     "--sysdepdir=\${prefix}/lib/skalibs/sysdeps"
-  ] ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ]);
+  ]
+  ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
+  # On darwin, the target triplet from -dumpmachine includes version number, but
+  # skarnet.org software uses the triplet to test binary compatibility.
+  # Explicitly setting target ensures code can be compiled against a skalibs
+  # binary built on a different version of darwin.
+  # http://www.skarnet.org/cgi-bin/archive.cgi?1:mss:623:heiodchokfjdkonfhdph
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   meta = {
     homepage = http://skarnet.org/software/skalibs/;

pkgs/tools/misc/execline/default.nix

@@ -25,7 +25,9 @@ in stdenv.mkDerivation rec {
     "--with-include=${skalibs}/include"
     "--with-lib=${skalibs}/lib"
     "--with-dynlib=${skalibs}/lib"
-  ] ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ]);
+  ]
+  ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   meta = {
     homepage = http://skarnet.org/software/execline/;

pkgs/tools/misc/s6-portable-utils/default.nix

@@ -20,7 +20,8 @@ in stdenv.mkDerivation rec {
     "--with-include=${skalibs}/include"
     "--with-lib=${skalibs}/lib"
     "--with-dynlib=${skalibs}/lib"
-  ];
+  ]
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   meta = {
     homepage = http://www.skarnet.org/software/s6-portable-utils/;

pkgs/tools/networking/s6-dns/default.nix

@@ -25,7 +25,9 @@ in stdenv.mkDerivation rec {
     "--with-include=${skalibs}/include"
     "--with-lib=${skalibs}/lib"
     "--with-dynlib=${skalibs}/lib"
-  ] ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ]);
+  ]
+  ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   meta = {
     homepage = http://www.skarnet.org/software/s6-dns/;

pkgs/tools/networking/s6-networking/default.nix

@@ -32,7 +32,8 @@ in stdenv.mkDerivation rec {
     "--with-dynlib=${execline}/lib"
     "--with-dynlib=${s6}/lib"
     "--with-dynlib=${s6Dns}/lib"
-  ];
+  ]
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   meta = {
     homepage = http://www.skarnet.org/software/s6-networking/;

pkgs/tools/system/s6-rc/default.nix

@@ -29,7 +29,9 @@ in stdenv.mkDerivation rec {
     "--with-dynlib=${skalibs}/lib"
     "--with-dynlib=${execline}/lib"
     "--with-dynlib=${s6}/lib"
-  ] ++ [ (if stdenv.isDarwin then "--disable-shared" else "--enable-shared") ];
+  ]
+  ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   meta = {
     homepage = http://skarnet.org/software/s6-rc/;

pkgs/tools/system/s6/default.nix

@@ -26,7 +26,9 @@ in stdenv.mkDerivation rec {
     "--with-lib=${execline}/lib"
     "--with-dynlib=${skalibs}/lib"
     "--with-dynlib=${execline}/lib"
-  ] ++ [ (if stdenv.isDarwin then "--disable-shared" else "--enable-shared") ];
+  ]
+  ++ (if stdenv.isDarwin then [ "--disable-shared" ] else [ "--enable-shared" ])
+  ++ (stdenv.lib.optional stdenv.isDarwin "--target=${stdenv.system}");
 
   preBuild = ''
     substituteInPlace "src/daemontools-extras/s6-log.c" \