[llvm] [AArch64, ELF] Allow implicit $d/$x at section beginning (PR #99718)

[Fangrui Song via llvm-commits]

MaskRay wrote:

As suggested by a binutils global maintainer, Jan Beulich, `optimize-mapping-symbols` has been renamed to `optimize-mapsyms`.
I will add clangDriver support for `-Wa,--optimize-mapsyms` once this is approved.

While binutils aarch64 maintainer Richard hasn't yet endorsed the solution, I believe there's significant value in having this option
for users who don't (a) mix data and code or (b) mix data-in-code text sections before or after this patch.

This feature is for LLVM 20, not for 19.x release, so that I will have more time to convince Richard.
(Although there is a desire to have this early to benefit my downstream...)


https://github.com/llvm/llvm-project/pull/99718