OCamlbuild.0.15.0

[hhugo]

OCamlbuild 0.15.0 comes with first class support for native Windows ports of OCaml
(MinGW64-w64 and MSVC). This support was historically provided by
opam-repository-mingw.

• Misc: restore CI (unix, macos, windows)
  (Setup github actions for ocamlbuild ocamlbuild#328, Enable CI on windows and fix it. ocamlbuild#329, Switch to opam.2.2 ocamlbuild#336, Add macos to the CI ocamlbuild#349 by Hugo Heuzard)

• Remove degraded mode for windows
  (Use normal codepath for win32 ocamlbuild#333 by Hugo Heuzard)

• Remove light mode (Remove the light mode ocamlbuild#332 by Hugo Heuzard)
• Make the codebase work on windows native
  (Enable CI on windows and fix it. ocamlbuild#329, Use normal codepath for win32 ocamlbuild#333, Add a test case for custom preprocessor ocamlbuild#334, Fix hack for bash when computing commands. ocamlbuild#338, No longer call into cmd.exe to execute a posix shell on windows ocamlbuild#339, Don't raise in sys_command_win32 ocamlbuild#342, nicer cmd on windows ocamlbuild#343, Add a tests for long commands  ocamlbuild#344 by Hugo Heuzard)

• No longer treat empty path in PATH env variable as the current working directory
  (No longer call into cmd.exe to execute a posix shell on windows ocamlbuild#339 by Hugo Heuzard)

• Emit a warning if several calls are made to
  Ocamlbuild_plugin.dispatch -- all calls before the last one are
  ignored, which may not be what users expect.
  ([RFC] warn on second call to the dispatch function ocamlbuild#30 by Gabriel Scherer, review by whitequark)
• Rename user-rebindable {LINK,COMP}FLAGS into OCB_{LINK,COMP}FLAGS
  (rename user-rebindable {LINK,COMP}FLAGS into OCB_{LINK,COMP}FLAGS ocamlbuild#303 by Gabriel Scherer)

[hhugo]

Some rev deps testing has been performed on windows. I could not identify any error caused by ocamlbuild

[hhugo]

ocaml/ocamlbuild#348

[hhugo]

I went through the logs and couldn't identify any error causes by ocamlbuild

[mseri]

A number of packages need fixing some bounds but these are all independent from ocamlbuild. I am going to merge and slowly in the future will send PR to fix the bounds

[mseri]

Thanks