[llvm] [CI] Disable PIE on Linux Premerge Builds (PR #154584)

[Derek Schuff via llvm-commits]

dschuff wrote:

I think this is pretty reasonable. PIE improves ASLR, reducing the ability of a binary to be exploited, but for PRs, people can write whatever code they want into LLVM and we will happily compile and execute it :D 
So if there's a performance win, LGTM

https://github.com/llvm/llvm-project/pull/154584