[llvm] [BOLT] support mold linker generated PLT in disassembling (PR #115256)

[Patrick Zhang via llvm-commits]

patrickphzhang wrote:

Following the suggestion of @tcwzxx, I have re-implemented the patch as follows:
1. Set the initial **offset** to 0.
2. Check if the section name is exactly '.plt' to skip other sections like '.plt.sec'.
    1) Disassemble the first instruction;
    2) Check if the first instruction is an `endbr`.
    3) Update the **offset** to 32 (mold plt header size) if it is.
3. Disassemble the PLT section from the **offset**.

Please review the code and let me know if any other changes are needed.

https://github.com/llvm/llvm-project/pull/115256