MemoryPacking: Removing empty segments can remove a trap

[kripken]

(module
 (memory $0 16 17)
 (data $0 (i32.const -1) "")
)

$ bin/wasm-opt a.wat --memory-packing --print
(module
 (memory $0 16 17)
)

Before the optimization this module traps during startup, as the segment offset is out of bounds.

We should probably make MemoryPacking not remove such segments unless TrapsNeverHappen is set, but perhaps there is a better idea?

[kripken]

This is also an issue in remove-unused-module-elements:

(module
 (import "fuzzing-support" "log-i32" (func $fimport$0 (param i32)))

 (memory $0 16 17 shared)
 (data $1 (i32.const -1) "")

 (export "func_13_invoker" (func $0))

 (func $0
  (call $fimport$0
   (i32.const 0)
  )
 )
)

$ bin/wasm-opt a.wat -all --fuzz-exec --remove-unused-module-elements
[trap out of bounds memory access in memory.init]
[fuzz-exec] calling func_13_invoker
[LoggingExternalInterface logging 0]
logging counts not identical!
[fuzz-exec] optimization passes changed results