std: allow overriding install dir of artifacts
std: allow overriding install dir of artifacts

This is necessary when, for example, writing a PAM module which should
be installed to lib/security/module_name.so.

raulgrell/zig,raulgrell/zig,raulgrell/zig,andrewrk/zig,raulgrell/zig,zig-lang/zig,zig-lang/zig,zig-lang/zig,andrewrk/zig,raulgrell/zig