message: fixes 1937 : reduces compile time.
  This commit prevents llvm optimization passes to be run on __keep_func_live()
  which is a temporary function created by ISPC to prevent certain pseudo functions etc.
  from being removed.
diff: @@ -4519,7 +4519,7 @@ declare void @__usedouble(<WIDTH x double>)
  define void @__keep_funcs_live(i8 * %ptr, <WIDTH x i8> %v8, <WIDTH x i16> %v16,
  <WIDTH x i32> %v32, <WIDTH x i64> %v64,
  - <WIDTH x MASK> %mask) {
  + <WIDTH x MASK> %mask) noinline optnone {
  ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
  ;; loads
  %ml8 = call <WIDTH x i8> @__masked_load_i8(i8 * %ptr, <WIDTH x MASK> %mask)
  