update fbcode to supercaml 1.26
Summary:
Enables supercaml 1.26 which updates ocaml to 4.12.1+fp+flambda
This diff must fix all projects using supercaml, most notably Hack, Flow, Pyre and Bigcode
About hack's dune build: I removed our mini repo build script to reuse the one from supercaml, which makes patching ocaml easier with the changes introduced by 4.12 (now +fp and +flambda are just regular packages).
Reviewed By: shayne-fletcher
Differential Revision:
D31569961
fbshipit-source-id:
7afe7a27e24e7989135dc624c6b0dd3c1a60a8f4