lib: Consolidate platform configurations (used for crossSystem)

This is good for maintenance and education.

lib/systems/default.nix

@@ -5,6 +5,7 @@ rec {
   parse = import ./parse.nix;
   inspect = import ./inspect.nix;
   platforms = import ./platforms.nix;
+  examples = import ./examples.nix;
 
   # Elaborate a `localSystem` or `crossSystem` so that it contains everything
   # necessary.

lib/systems/examples.nix

@@ -0,0 +1,130 @@
+# These can be passed to nixpkgs as either the `localSystem` or
+# `crossSystem`. They are put here for user convenience, but also used by cross
+# tests and linux cross stdenv building, so handle with care!
+
+let platforms = import ./platforms.nix; in
+
+rec {
+  #
+  # Linux
+  #
+
+  sheevaplug = rec {
+    config = "armv5te-unknown-linux-gnueabi";
+    bigEndian = false;
+    arch = "armv5te";
+    float = "soft";
+    withTLS = true;
+    libc = "glibc";
+    platform = platforms.sheevaplug;
+    openssl.system = "linux-generic32";
+    inherit (platform) gcc;
+  };
+
+  raspberryPi = rec {
+    config = "armv6l-unknown-linux-gnueabihf";
+    bigEndian = false;
+    arch = "armv6l";
+    float = "hard";
+    fpu = "vfp";
+    withTLS = true;
+    libc = "glibc";
+    platform = platforms.raspberrypi;
+    openssl.system = "linux-generic32";
+    inherit (platform) gcc;
+  };
+
+  armv7l-hf-multiplatform = rec {
+    config = "arm-unknown-linux-gnueabihf";
+    bigEndian = false;
+    arch = "armv7-a";
+    float = "hard";
+    fpu = "vfpv3-d16";
+    withTLS = true;
+    libc = "glibc";
+    platform = platforms.armv7l-hf-multiplatform;
+    openssl.system = "linux-generic32";
+    inherit (platform) gcc;
+  };
+
+  aarch64-multiplatform = rec {
+    config = "aarch64-unknown-linux-gnu";
+    bigEndian = false;
+    arch = "aarch64";
+    withTLS = true;
+    libc = "glibc";
+    platform = platforms.aarch64-multiplatform;
+    inherit (platform) gcc;
+  };
+
+  scaleway-c1 = armv7l-hf-multiplatform // rec {
+    platform = platforms.scaleway-c1;
+    inherit (platform) gcc;
+    inherit (gcc) fpu;
+  };
+
+  pogoplug4 = rec {
+    arch = "armv5tel";
+    config = "armv5tel-softfloat-linux-gnueabi";
+    float = "soft";
+
+    platform = platforms.pogoplug4;
+
+    inherit (platform) gcc;
+    libc = "glibc";
+
+    withTLS = true;
+    openssl.system = "linux-generic32";
+  };
+
+  fuloongminipc = rec {
+    config = "mips64el-unknown-linux-gnu";
+    bigEndian = false;
+    arch = "mips";
+    float = "hard";
+    withTLS = true;
+    libc = "glibc";
+    platform = platforms.fuloong2f_n32;
+    openssl.system = "linux-generic32";
+    inherit (platform) gcc;
+  };
+
+  #
+  # Darwin
+  #
+
+  iphone64 = {
+    config = "aarch64-apple-darwin14";
+    arch = "arm64";
+    libc = "libsystem";
+    platform = {};
+  };
+
+  iphone32 = {
+    config = "arm-apple-darwin10";
+    arch = "armv7-a";
+    libc = "libsystem";
+    platform = {};
+  };
+
+  #
+  # Windows
+  #
+
+  # 32 bit mingw-w64
+  mingw32 = {
+    config = "i686-pc-mingw32";
+    arch = "x86"; # Irrelevant
+    libc = "msvcrt"; # This distinguishes the mingw (non posix) toolchain
+    platform = {};
+  };
+
+  # 64 bit mingw-w64
+  mingwW64 = {
+    # That's the triplet they use in the mingw-w64 docs.
+    config = "x86_64-pc-mingw32";
+    arch = "x86_64"; # Irrelevant
+    libc = "msvcrt"; # This distinguishes the mingw (non posix) toolchain
+    platform = {};
+  };
+}

lib/systems/platforms.nix

@@ -255,6 +255,10 @@ rec {
       arch = "armv6";
       fpu = "vfp";
       float = "hard";
+      # TODO(@Ericson2314) what is this and is it a good idea? It was
+      # used in some cross compilation examples but not others.
+      #
+      # abi = "aapcs-linux";
     };
   };
 
@@ -460,7 +464,10 @@ rec {
     '';
     kernelTarget = "vmlinux";
     uboot = null;
-    gcc.arch = "loongson2f";
+    gcc = {
+      arch = "loongson2f";
+      abi = "n32";
+    };
   };
 
   beaglebone = armv7l-hf-multiplatform // {