nixpkgs: hhvm 3.3.0 -> 3.6.0
nixpkgs: hhvm 3.3.0 -> 3.6.0

  - We need {perl,git,krb5,libvpx,etc} as a dependency
  - Drop upstream patches.
  - Simplify build (uses cmake configuration)
  - Simplify install (uses cmake generated installer)

Signed-off-by: Austin Seipp <48c905ac3851f382b914247d97dd93273d5ff555@pobox.com>

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