When doing Zero VM performance investigations, I realized that UseTLAB is disabled there by default. That is because UseTLAB is currently product_pd (in gc_globals), and it is enabled for every platform with c1 and c2 ports (in their respective c1/c2_globals). compiler_globals has a block that defines UseTLAB to false when no C1/C2/JVMCI is present.

Not only this is awkward -- GC flag is managed by Compiler globals! -- it makes Zero hard to opt-in to UseTLAB by default, because compiler_globals already define it.

I think we can make this all better by turning TLAB flags from product_pd to product, and defaulting them to "true".