[clang] [lld] [llvm] [X86] Implement disabling APX relocations and EPGR/NDD instrs for relocations (PR #136660)

[Shengchen Kan via llvm-commits]

KanRobert wrote:

> Introduce an option (-mapx-relax-relocations) to control the emission of the new APX relocations. It's off by default to keep backward compatibility with old version of ld and other linkers without APX support. And EGPR and NDD are also suppressed to avoid the instructions updated incorrectly by old version of linkers.

Not understand this. IIUC, either we should not emit APX instructions at all, which  is controlled by `-m[no-]apxf`, or we should not relax the all the relocations, which is controlled by `-Wl,--no-relax`.

https://github.com/llvm/llvm-project/pull/136660