Add msystem support on msys2

[star-hengxing]

Is your feature request related to a problem? Please describe.

target("ucrt64")
    set_arch("x86_64")
    set_kind("binary")
    add_files("src/*.c")
    set_toolchains("mingw", {msystem = "ucrt64"})
--     set_toolchains("clang", {msystem = "ucrt64"})
target("mingw32")
    set_arch("i686")
    set_kind("binary")
    add_files("src/*.c")
    set_toolchains("mingw", {msystem = "mingw32"})
--     set_toolchains("clang", {msystem = "mingw32"})

related #6128

Describe the solution you'd like

#6884

toolchains

• mingw
• clang

Describe alternatives you've considered

No response

Additional context

No response