add flatbuffers (#197)

* add flatbuffers

* fix mingw on macos

packages/f/flatbuffers/xmake.lua

@@ -0,0 +1,31 @@
+package("flatbuffers")
+
+    set_homepage("http://google.github.io/flatbuffers/")
+    set_description("FlatBuffers is a cross platform serialization library architected for maximum memory efficiency.")
+
+    add_urls("https://github.com/google/flatbuffers/archive/v$(version).zip")
+    add_versions("1.12.0", "4b8b21adbfe8a74b90604161afcf87c125a26b86c99327e7a04525080606536c")
+
+    add_deps("cmake")
+    on_install("windows", "linux", "macosx", "mingw", "android", "iphoneos", function(package)
+        local configs = {"-DFLATBUFFERS_BUILD_TESTS=OFF"}
+        if is_plat("android", "iphoneos") then
+            table.insert(configs, "-DFLATBUFFERS_BUILD_FLATC=OFF")
+            table.insert(configs, "-DFLATBUFFERS_BUILD_FLATHASH=OFF")
+        end
+        import("package.tools.cmake").install(package, configs)
+        package:addenv("PATH", "bin")
+    end)
+
+    on_test(function(package)
+        if is_plat("windows", "linux", "macosx", "mingw@windows") then
+            os.vrun("flatc --version")
+        end
+        assert(package:check_cxxsnippets({test = [[
+            void test() {
+                flatbuffers::FlatBufferBuilder builder;
+                builder.CreateString("MyMonster");
+                flatbuffers::DetachedBuffer dtbuilder = builder.Release();
+            }
+        ]]}, {configs = {languages = "c++14"}, includes = "flatbuffers/flatbuffers.h"}))
+    end)