[llvm] [llvm][EmbedBitcodePass] Prevent modifying the module with ThinLTO (PR #139999)

[Tom Stellard via llvm-commits]

tstellar wrote:

@ilovepi I've bisected a crash down to this commit.  Attached is a reproducer: 
[proactor_test-f405d8.cpp.txt](https://github.com/user-attachments/files/20847114/proactor_test-f405d8.cpp.txt)
[proactor_test-f405d8.sh.txt](https://github.com/user-attachments/files/20847115/proactor_test-f405d8.sh.txt)


https://github.com/llvm/llvm-project/pull/139999