[llvm] Initialize PreferredAlign in Function (PR #192156)

[Eli Friedman via llvm-commits]

efriedma-quic wrote:

Valgrind is known to be incompatible with the way compilers lower certain constructs; we aren't going to work around Valgrind false positives.  (We would consider adding a clang flag that tries to generate Valgrind-compatible code, if someone wants to implement that.)

https://github.com/llvm/llvm-project/pull/192156