store target.min_global_align as an Align

[folkertdev]

Parse the alignment properly when the target is defined/parsed, and error out on invalid alignment values. That means this work doesn't need to happen for every global in each backend.

[rustbot]

r? @wesleywiser

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[rustbot]

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

These commits modify compiler targets.
(See the Target Tier Policy.)

[workingjubilee]

@bors r+ rollup

[bors]

📌 Commit a50bd7c has been approved by workingjubilee

It is now in the queue for this repository.