Add a top-level --with-system-libs arg to build.sh

[omajid]

This lets users build the VMR with a top-level flag like this:

$ /build.sh --source-only --with-system-libs brotli+libunwind+rapidjson+zlib

This was suggested during PR review at:
#41984 (comment)

[omajid]

cc @akoeplinger

[omajid]

Does it also make sense to support the plain argument to default all libs to come from system so the distros don't need to chase adding new ones when we add new dependencies?

I thought about this and have mixed feelings about this. On one hand, like you say, it will help some distros. On the other hand, a number of distros I tried out wont be able to use all. For example. on Fedora, I will not be able to use system libunwind on arm64. On RHEL, I will not be able to use system rapidjson.

Maybe it would be better to document this better?

What about adding top-level flag for each library separately, like this:

./build.sh --with-system-brotli --with-system-libunwind --with-system-rapidjson --with-system-zlib

And these top-level flags would be document via ./build.sh --help.

[akoeplinger]

What about adding top-level flag for each library separately, like this

That's the same then as listing each lib in --with-system-libs so doesn't provide much benefit and we'd need to touch the script everytime we add a lib. Given an "all" concept doesn't really work given what you said about distro differences I think the current approach makes the most sense.

[tmds]

Does it also make sense to support the plain argument to default all libs to come from system so the distros don't need to chase adding new ones when we add new dependencies?

My 2 cents.

I think the default experience should match with what a distro maintainer probably prefers: system libs or bundled libs.

If we think that preference is system libs, it would make sense the argument controls what bundled libs to use instead of what system libs.