Don't inline dynamic allocas that simplify to huge static allocas.
Some sequences of optimizations can generate call sites which may never be executed during runtime, and through constant propagation result in dynamic allocas being converted to static allocas with very large allocation amounts. The inliner tries to move these to the caller's entry block, resulting in the stack limits being reached/bypassed. Avoid inlining functions if this would result. The threshold of 64k currently doesn't get triggered on the test suite with an -Os LTO build on arm64, care should be taken in changing this in future to avoid needlessly pessimising inlining behaviour. Differential Revision: https://reviews.llvm.org/D81765