x86_64: inline and global assembly features are incomplete

[jacobly0]

Specifically, there is a disabled behavior test for global asm that does not seem worth supporting at this time. Any required symbol properties should be implemented in std.builtin.ExternOptions and std.builtin.ExportOptions instead, as the language assembly features have a planned redesign anyway and it is unclear what features will be available in the new design.

[andrewrk]

Related:

• parse inline assembly syntax according to a set of dialects; integrate inline assembly more closely with the zig language #10761