wasm: init cross target

Adds pkgsCross.wasm32 and pkgsCross.wasm64. Use it to build Nixpkgs
with a WebAssembly toolchain.

stdenv/cross: use static overlay on isWasm

isWasm doesn’t make sense dynamically linked.

lib/systems/default.nix

@@ -30,6 +30,7 @@ rec {
       libc =
         /**/ if final.isDarwin              then "libSystem"
         else if final.isMinGW               then "msvcrt"
+        else if final.isWasi                then "wasilibc"
         else if final.isMusl                then "musl"
         else if final.isUClibc              then "uclibc"
         else if final.isAndroid             then "bionic"
@@ -62,7 +63,7 @@ rec {
           "netbsd" = "NetBSD";
           "freebsd" = "FreeBSD";
           "openbsd" = "OpenBSD";
-          "wasm" = "Wasm";
+          "wasi" = "Wasi";
         }.${final.parsed.kernel.name} or null;
 
          # uname -p

lib/systems/doubles.nix

@@ -17,6 +17,8 @@ let
     "x86_64-netbsd" "x86_64-openbsd" "x86_64-solaris"
 
     "x86_64-windows" "i686-windows"
+
+    "wasm64-wasi" "wasm32-wasi"
   ];
 
   allParsed = map parse.mkSystemFromString all;
@@ -45,6 +47,7 @@ in rec {
   netbsd  = filterDoubles predicates.isNetBSD;
   openbsd = filterDoubles predicates.isOpenBSD;
   unix    = filterDoubles predicates.isUnix;
+  wasi    = filterDoubles predicates.isWasi;
   windows = filterDoubles predicates.isWindows;
 
   mesaPlatforms = ["i686-linux" "x86_64-linux" "x86_64-darwin" "armv5tel-linux" "armv6l-linux" "armv7l-linux" "armv7a-linux" "aarch64-linux" "powerpc64le-linux"];

lib/systems/examples.nix

@@ -116,7 +116,7 @@ rec {
     config = "aarch64-none-elf";
     libc = "newlib";
   };
-  
+
   aarch64be-embedded = {
     config = "aarch64_be-none-elf";
     libc = "newlib";
@@ -126,7 +126,7 @@ rec {
     config = "powerpc-none-eabi";
     libc = "newlib";
   };
-  
+
   ppcle-embedded = {
     config = "powerpcle-none-eabi";
     libc = "newlib";
@@ -211,4 +211,14 @@ rec {
     config = "x86_64-unknown-netbsd";
     libc = "nblibc";
   };
+
+  #
+  # WASM
+  #
+
+  wasi32 = {
+    config = "wasm32-unknown-wasi";
+    useLLVM = true;
+  };
+
 }

lib/systems/for-meta.nix

@@ -32,6 +32,7 @@ in rec {
   openbsd = [ patterns.isOpenBSD ];
   unix    = patterns.isUnix; # Actually a list
   windows = [ patterns.isWindows ];
+  wasi    = [ patterns.isWasi ];
 
   inherit (lib.systems.doubles) mesaPlatforms;
 }

lib/systems/inspect.nix

@@ -43,9 +43,10 @@ rec {
     isWindows      = { kernel = kernels.windows; };
     isCygwin       = { kernel = kernels.windows; abi = abis.cygnus; };
     isMinGW        = { kernel = kernels.windows; abi = abis.gnu; };
+    isWasi         = { kernel = kernels.wasi; };
 
     isAndroid      = [ { abi = abis.android; } { abi = abis.androideabi; } ];
-    isMusl         = with abis; map (a: { abi = a; }) [ musl musleabi musleabihf ];
+    isMusl         = (with abis; map (a: { abi = a; }) [ musl musleabi musleabihf ]) ++ [{ kernel = kernels.wasi; }];
     isUClibc       = with abis; map (a: { abi = a; }) [ uclibc uclibceabi uclibceabihf ];
 
     isEfi          = map (family: { cpu.family = family; })

lib/systems/parse.nix

@@ -226,6 +226,7 @@ rec {
     elf = {};
     macho = {};
     pe = {};
+    wasm = {};
 
     unknown = {};
   };
@@ -268,6 +269,7 @@ rec {
     none    = { execFormat = unknown; families = { }; };
     openbsd = { execFormat = elf;     families = { inherit bsd; }; };
     solaris = { execFormat = elf;     families = { }; };
+    wasi    = { execFormat = wasm;    families = { }; };
     windows = { execFormat = pe;      families = { }; };
   } // { # aliases
     # 'darwin' is the kernel for all of them. We choose macOS by default.
@@ -376,6 +378,8 @@ rec {
         then { cpu = elemAt l 0;                      kernel = elemAt l 1; abi = elemAt l 2; }
       else if (elemAt l 2 == "mingw32") # autotools breaks on -gnu for window
         then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "windows";                    }
+      else if (elemAt l 2 == "wasi")
+        then { cpu = elemAt l 0; vendor = elemAt l 1; kernel = "wasi";                       }
       else if hasPrefix "netbsd" (elemAt l 2)
         then { cpu = elemAt l 0; vendor = elemAt l 1;    kernel = elemAt l 2;                }
       else if (elem (elemAt l 2) ["eabi" "eabihf" "elf"])