Add emscripten (#2263)

* Add emscripten

* Use find_directory

* Apply review comment

packages/e/emscripten/xmake.lua

@@ -0,0 +1,56 @@
+package("emscripten")
+
+    set_kind("toolchain")
+    set_homepage("https://emscripten.org/")
+    set_description("Emscripten: An LLVM-to-WebAssembly Compiler.")
+    set_license("MIT")
+
+    set_urls("https://github.com/emscripten-core/emsdk.git")
+    add_versions("3.1.42", "c2260b4f28f53b411032de0955a6fe6b6bcf3edd")
+
+    add_deps("python")
+
+    on_install("windows", "macosx", "linux", function (package)
+
+        import("lib.detect.find_directory")
+		-- copy to installdir
+        os.cp("*", package:installdir())
+	
+        -- installation
+        local version = package:version():rawstr()
+        local installdir = package:installdir()
+        local py = package:is_plat("windows") and "python" or "python3"
+        os.vrunv(py, {path.join(installdir, "emsdk.py"), "install", version})
+
+        -- activation
+        os.vrunv(py, {path.join(installdir, "emsdk.py"), "activate", version})
+
+        -- setup env
+        package:addenv("PATH", node)
+        package:addenv("PATH", path.join(installdir, "upstream", "emscripten"))
+        package:addenv("PATH", installdir)
+        package:addenv("EMSDK", installdir)
+    
+        local exe = package:is_plat("windows") and ".exe" or ""
+        local node = find_directory("bin", {path.join(installdir, "node", "**")})
+        if node then
+            package:addenv("PATH", node)
+            package:addenv("EMSDK_NODE", path.join(node, "node" .. exe))
+        end
+
+        if package:is_plat("windows") then
+            local python = find_directory("*", path.join(installdir, "python"))
+            if python then
+                package:addenv("EMSDK_PYTHON", path.join(python, "python" .. exe))
+            end
+            local java = find_directory("*", path.join(installdir, "java"))
+            if java then
+                package:addenv("JAVA_HOME", java)
+            end
+        end
+    end)
+
+    on_test(function (package)
+        local emcc = is_host("windows") and "emcc.bat" or "emcc"
+        os.vrunv(emcc, {"--version"})
+    end)