Remove more cruft from fx_system.h

- include system headers first and alphabetize.
- remove unsupported FX_WIN32_MOBILE symbol.
- actually define  a FX_WIN64 symbol and make consistent.
- use final/override, not FX_FINAL.
- let stdint.h resolve FX_WORDSIZE concerns.
- unused FX_ERR and FX_SUCCESS() macros.
- unused FX_LSB_FIRST macro.
- outline FX type deprecation plan.

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1169963003
20 files changed