a414877a7a
This is the x64 equivalent of #121516 Since import call optimization was originally [added to x64 Windows to implement a more efficient retpoline mitigation](https://techcommunity.microsoft.com/blog/windowsosplatform/mitigating-spectre-variant-2-with-retpoline-on-windows/295618) the section and constant names relating to this all mention "retpoline" and we need to mark indirect calls, control-flow guard calls and jumps for jump tables in the section alongside calls to imported functions. As with the AArch64 feature, this emits a new section into the obj which is used by the MSVC linker to generate the Dynamic Value Relocation Table and the section itself does not appear in the final binary. The Windows Loader requires a specific sequence of instructions be emitted when this feature is enabled: * Indirect calls/jumps must have the function pointer to jump to in `rax`. * Calls to imported functions must use the `rex` prefix and be followed by a 5-byte nop. * Indirect calls must be followed by a 3-byte nop.
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