[bug] Wrong auto path_flavor in tools.unix_path if MinGW installed with Msys2

[SpaceIm]

Environment Details (include every applicable attribute)

• Operating System+version: Windows 10
• Compiler+version: gcc10
• Conan version: 1.32.0
• Python version: 3.7.1

Steps to reproduce (Include if Applicable)

• Install MinGW with msys2.
• On Windows, build a recipe relying on environment variables defined in package_info() of autoconf recipe in CCI (libxcrypt for example: [package] libxcrypt/4.4.16: build fails on Windows with MinGW conan-center-index#3356). These environment variables use tools.unix_path() with default path_flavor
  => /mnt will be added to path, leading to error. I guess that it detects WSL for some weird reason:

  conan/conans/client/tools/win.py

  Line 624 in 61d75d9

  return '/mnt' + path[0:2].lower() + path[2:]

  )

Surprinsingly, if I download a prebuild mingw without msys2, I can't reproduce this error (but I've tested on another computer with WSL disabled).

Logs (Executed commands with output) (Include/Attach if Applicable)

/usr/bin/bash: /mnt/c/Users/spaceim/.conan/data/autoconf/2.69/_/_/package/ca33edce272a279b24f87dc0d4cf5bbdcffbc187/bin/autoreconf.exe: No such file or directory