[llvm] [Offload] Cache symbols in program (PR #148209)

[Joseph Huber via llvm-commits]

https://github.com/jhuber6 commented:

Every symbol lookup is going to search an O(N) list? It would be faster to just use the ELF's symbol table at that point because it's hashed. Shouldn't we be able to use a map or something?

https://github.com/llvm/llvm-project/pull/148209