Add .enable_wasmtime build flag

lib/std/build.zig

@@ -1064,6 +1064,9 @@ pub const LibExeObjStep = struct {
     /// Uses system QEMU installation to run cross compiled foreign architecture build artifacts.
     enable_qemu: bool = false,
 
+    /// Uses system Wasmtime installation to run cross compiled wasm/wasi build artifacts.
+    enable_wasmtime: bool = false,
+
     /// After following the steps in https://github.com/ziglang/zig/wiki/Updating-libc#glibc,
     /// this will be the directory $glibc-build-dir/install/glibcs
     /// Given the example of the aarch64 target, this is the directory
@@ -1863,6 +1866,11 @@ pub const LibExeObjStep = struct {
                 try zig_args.append(bin_name);
                 try zig_args.append("--test-cmd-bin");
             },
+            .wasm => |bin_name| if (self.enable_wasm) {
+                try zig_args.append("--test-cmd");
+                try zig_args.append(bin_name);
+                try zig_args.append("--test-cmd-bin");
+            },
         }
         for (self.packages.toSliceConst()) |pkg| {
             zig_args.append("--pkg-begin") catch unreachable;

lib/std/target.zig

@@ -611,6 +611,7 @@ pub const Target = union(enum) {
         native,
         qemu: []const u8,
         wine: []const u8,
+        wasmtime: []const u8,
         unavailable,
     };
 
@@ -649,6 +650,13 @@ pub const Target = union(enum) {
             }
         }
 
+        if (self.isWasm()) {
+            switch (self.getArchPtrBitWidth()) {
+                32 => return Executor{ .wasmtime = "wasmtime" },
+                else => return .unavailable,
+            }
+        }
+
         return .unavailable;
     }
 };