Ensure ASM syntax detect global_asm! and asm! only on x86 architectures

[beetrees]

The ASM syntax lint is only relevant on x86 architectures, so this PR ensures it doesn't trigger on other architectures. This PR also makes the lints check global_asm! items as well as asm! expressions.

changelog: Check global_asm! items in the ASM syntax lints, and fix false positives on non-x86 architectures.

[rustbot]

r? @Manishearth

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[Manishearth]

Not 100% convinced this is the way to do it but I can't see an easier way to detect cfgs.

[Manishearth]

@bors r+

oh I somehow missed it was used twice

but this is fine for now

[bors]

📌 Commit 9b5e4c6 has been approved by Manishearth

It is now in the queue for this repository.

[bors]

⌛ Testing commit 9b5e4c6 with merge 5471e06...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Manishearth
Pushing 5471e06 to master...