Add isdefined check count_const_size

This doesn't do much currently, because we only call this function
on `Const` objects which we don't currently create if the initialization
of the object is incomplete, but we may want to do so in the future,
so might as well be defensive about it.

(cherry picked from commit 1327b5c)

base/compiler/utilities.jl

@@ -82,6 +82,7 @@ function count_const_size(@nospecialize(x))
  dtfd = DataTypeFieldDesc(dt)
  for i = 1:nfields(x)
  dtfd[i].isptr || continue
+ isdefined(x, i) || continue
  sz += count_const_size(getfield(x, i))
  sz > MAX_INLINE_CONST_SIZE && return MAX_INLINE_CONST_SIZE + 1
  end

test/compiler/inline.jl

@@ -324,3 +324,9 @@ let ci = code_typed(NonIsBitsDims, Tuple{})[1].first
  @test length(ci.code) == 1 && isa(ci.code[1], ReturnNode) &&
  ci.code[1].val.value == NonIsBitsDims()
 end
+
+struct NonIsBitsDimsUndef
+ dims::NTuple{N, Int} where N
+ NonIsBitsDimsUndef() = new()
+end
+@test Core.Compiler.is_inlineable_constant(NonIsBitsDimsUndef())