[llvm] [AArch64] Always add PURECODE flag to empty .text if "+execute-only" is set (PR #132196)

[Csanád Hajdú via llvm-commits]

Il-Capitano wrote:

Yeah, I'm not sure why it's that way in the ARM backend. A similar mechanism is needed in Target/ARM/MCTargetDesc/ARMELFStreamer.cpp (and AArch64ELFStreamer.cpp too), where it also modifies the flags on the existing section:
https://github.com/llvm/llvm-project/blob/382b707e52ee6a0ca9a799795362dee67ade993f/llvm/lib/Target/ARM/MCTargetDesc/ARMELFStreamer.cpp#L1136-L1154

https://github.com/llvm/llvm-project/pull/132196