improve xcode

Author: waruqi

xmake/toolchains/xcode/xmake.lua

@@ -40,14 +40,14 @@ toolchain("xcode")
         local xc_dsymutil       = bindir and path.join(bindir, "dsymutil") or "dsymutil"
 
         toolchain:set("toolset", "cc", xc_clang)
-        toolchain:set("toolset", "cxx", xc_clang, xc_clangxx)
+        toolchain:set("toolset", "cxx", xc_clangxx, xc_clang)
         toolchain:set("toolset", "ld", xc_clangxx, xc_clang)
         toolchain:set("toolset", "sh", xc_clangxx, xc_clang)
         toolchain:set("toolset", "ar", xc_ar)
         toolchain:set("toolset", "strip", xc_strip)
         toolchain:set("toolset", "dsymutil", xc_dsymutil, "dsymutil")
         toolchain:set("toolset", "mm", xc_clang)
-        toolchain:set("toolset", "mxx", xc_clang, xc_clangxx)
+        toolchain:set("toolset", "mxx", xc_clangxx, xc_clang)
         toolchain:set("toolset", "sc", xc_swift_frontend, "swift_frontend", xc_swiftc, "swiftc")
         toolchain:set("toolset", "scld", xc_swiftc, "swiftc")
         toolchain:set("toolset", "scsh", xc_swiftc, "swiftc")