improve boost for mingw (#1809)

* improve boost for mingw

* improve boost

* improve boost

packages/b/boost/xmake.lua

@@ -149,10 +149,13 @@ package("boost")
             "--libdir=" .. package:installdir("lib"),
             "--without-icu"
         }
-        if is_host("windows") then
+        if package:is_plat("windows") then
             import("core.tool.toolchain")
             local runenvs = toolchain.load("msvc"):runenvs()
             os.vrunv("bootstrap.bat", bootstrap_argv, {envs = runenvs})
+        elseif package:is_plat("mingw") and is_host("windows") then
+            os.vrunv("sh", table.join("./bootstrap.sh", bootstrap_argv))
+            os.cp("./tools/build/src/engine/b2.exe", ".")
         else
             os.vrunv("./bootstrap.sh", bootstrap_argv)
         end