Change compilers priority for gcc and clang

Before this change xmake preferred to use clang and gcc for c++ code which caused build to fail with clang in my current setup

Author: Dmitry Malakhov

xmake/toolchains/clang/xmake.lua

@@ -31,15 +31,15 @@ toolchain("clang" .. suffix)
     set_runtimes("c++_static", "c++_shared", "stdc++_static", "stdc++_shared")
 
     set_toolset("cc",      "clang" .. suffix)
-    set_toolset("cxx",     "clang" .. suffix, "clang++" .. suffix)
+    set_toolset("cxx",     "clang++" .. suffix, "clang" .. suffix)
     set_toolset("ld",      "clang++" .. suffix, "clang" .. suffix)
     set_toolset("sh",      "clang++" .. suffix, "clang" .. suffix)
     set_toolset("ar",      "ar",      "llvm-ar" .. suffix)
     set_toolset("strip",   "strip",   "llvm-strip" .. suffix)
     set_toolset("ranlib",  "ranlib",  "llvm-ranlib" .. suffix)
     set_toolset("objcopy", "objcopy", "llvm-objcopy" .. suffix)
     set_toolset("mm",      "clang" .. suffix)
-    set_toolset("mxx",     "clang" .. suffix, "clang++" .. suffix)
+    set_toolset("mxx",     "clang++" .. suffix, "clang" .. suffix)
     set_toolset("as",      "clang" .. suffix)
     set_toolset("mrc",     "llvm-rc" .. suffix)
     set_toolset("dlltool", "llvm-dlltool" .. suffix)

xmake/toolchains/gcc/xmake.lua

@@ -31,15 +31,15 @@ toolchain("gcc" .. suffix)
     set_runtimes("stdc++_static", "stdc++_shared")
 
     set_toolset("cc", "gcc" .. suffix)
-    set_toolset("cxx", "gcc" .. suffix, "g++" .. suffix)
+    set_toolset("cxx", "g++" .. suffix, "gcc" .. suffix)
     set_toolset("ld", "g++" .. suffix, "gcc" .. suffix)
     set_toolset("sh", "g++" .. suffix, "gcc" .. suffix)
     set_toolset("ar", "ar")
     set_toolset("strip", "strip")
     set_toolset("objcopy", "objcopy")
     set_toolset("ranlib", "ranlib")
     set_toolset("mm", "gcc" .. suffix)
-    set_toolset("mxx", "gcc" .. suffix, "g++" .. suffix)
+    set_toolset("mxx", "g++" .. suffix, "gcc" .. suffix)
     set_toolset("as", "gcc" .. suffix)
 
     on_check(function (toolchain)

xmake/toolchains/llvm/xmake.lua

@@ -25,8 +25,8 @@ toolchain("llvm")
     set_runtimes("c++_static", "c++_shared", "stdc++_static", "stdc++_shared")
 
     set_toolset("cc",      "clang")
-    set_toolset("cxx",     "clang", "clang++")
-    set_toolset("mxx",     "clang", "clang++")
+    set_toolset("cxx",     "clang++", "clang")
+    set_toolset("mxx",     "clang++", "clang")
     set_toolset("mm",      "clang")
     set_toolset("cpp",     "clang -E")
     set_toolset("as",      "clang")