Automatically flag x86-64 asm object files as SHSTK-compatible.
Shadow Stack (SHSTK) is a part of Control-flow Enforcement Technology
(CET) which is a feature aimed at defending against ROP attacks by
verifying that 'call' and 'ret' instructions are correctly matched.
For well-written code this works transparently without any code changes,
as return addresses popped from the shadow stack should match return
addresses popped from the normal stack for performance reasons anyway.
Henrik Gramner
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