Improve to merge static library

[waruqi]

old solution

target("test")
    set_kind("static")
    add_files("src/*.a")

It does not support merging archive libraries containing .o files with the same name. And it is very inconvenient to merge dependent target libraries.

new solution

we use set_policy("build.merge_archive", true) to enable merge archive intead of linking for all dependent targets.

target("add")
    set_kind("static")
    add_files("src/add.c")

target("sub")
    set_kind("static")
    add_files("src/sub.c")

target("mul")
    set_kind("static")
    add_deps("add", "sub")
    add_files("src/mul.c")
    set_policy("build.merge_archive", true)

we can also call module script to merge static library.

target("test")
    after_link(function (target)
        import("utils.archive.merge_staticlib")
        merge_staticlib(target, "libout.a", {"libfoo.a", "libbar.a"})
    end)

[SirLynix]

What advantages are there to merge static libraries? Is it supported by all toolchains?

[waruqi]

What advantages are there to merge static libraries? Is it supported by all toolchains?

Some users only want to distribute a single static library externally, they don't want to provide too many static libraries.

Currently supports ar and msvc/lib.exe, and should be able to support most toolchains.