Rewrite `set_date_fields` to match the ECMA specification

Rewrite `set_date_fields` to match the ECMA specification

- use `double` arithmetic where necessary to match the spec
- use `volatile` to ensure correct order of evaluation
  and prevent FMA code generation
- reject some border cases.
- avoid undefined behavior in `double` -> `int64_t` conversions
- improved tests/test_builtin.js `assert` function to compare
  values more reliably.
- added some tests in `test_date()`
- disable some of these tests on win32 and cygwin targets