`-O2` changes the result of `==` between vector constants

[tidusec]

In a LUA_VECTOR_SIZE 3 build, a surplus 4th argument to vector.create affects ==
at -O2 but not at -O0/-O1.

print(vector.create(1, 2, 3) == vector.create(1, 2, 3, 9))

luau -O0  -->  true
luau -O1  -->  true
luau -O2  -->  false

Both sides print 1, 2, 3, and .x/.y/.z compare equal at every level.

Two more observations that may help narrow it:

• At -O2, == and rawequal disagree on the same pair:
  a == b is false while rawequal(a, b) is true.
• It only affects constant-folded operands. With
  local function mk(x,y,z) return vector.create(x,y,z) end,
  mk(1,2,3) == vector.create(1,2,3,9) is true at -O2.

Rebuilding the same source with LUA_VECTOR_SIZE 4 gives false at all three levels,
which is correct for a 4-wide build. The divergence is 3-wide only.

tests/conformance/vector.luau passes unmodified at -O0/-O1/-O2.