Difficulty building boost 1.62.0 using current mingw distribution

[drmhkelley@…]

This was really frustrating - am not experienced bat file user so don't know what the "proper" fixes would be. I fixed 3 specific issues.

1. bootstrap.bat never reached the section looking for MinGW gcc compiler. I moved that earlier in the script (just before checking for msvc compilers).
2. the path for the gcc compiler was hardwired - I had to modify the script to look in the right place and also properly adjust the value for the BOOST_JAM variable.
3. toolset=mingw is not supported by jam - had to set it to gcc instead
4. project-config.jam still had toolset=mingw, had to set it to gcc.

After those changes (and loss of *many* chunks of hair!!) bootstrap and b2 seem to be working correctly. Will update this ticket or post a new if further problems arise.