flexlink should cygpath %TEMP% before passing to bash

[dra27]

cd _boot && C:\ocamlmgw64\bin\ocamlopt.opt.exe -o ..\dune.exe -g -I +threads unix.cmxa threads.cmxa -no-alias-deps -w -49 fcntl_stubs.c -args mods_list
/bin/bash: C:UsersDRAAppDataLocalTemplongcmd7285c9: No such file or directory

Placeholder to check when I have more time, but changing TEMP to C:/Users/DRA/AppData/Local/Temp "fixed" the problem

[dra27]

Actually the forward-slash trick wasn't sufficient - full repro was to set-up a mingw64 compiler from a command prompt:

• set PATH=C:\ocamlmgw64\bin;C:\cygwin\usr\x86_64-w64-mingw32\bin;C:\cygwin\usr\x86_64-w64-mingw32\sys-root\mingw\bin;C:\cygwin\bin;%PATH
• Clone dune
• ocaml bootstrap.ml