BOOST THREAD macro

[Andreas Röver]

Hello,

I think I might have found 2 bugs in ax_boost_thread.m4:

- in the OS selection switches, where the special cases for mingw are
  selected, it says ming32 but should be mingw32
- those switches are supposed to be dependent on the os you compile for
  but the switch uses the build_os variable.

I've appended a modified file that fixes those 2 issues. Without them
cross compiling for Windows on Unix is not possible or requires manual
patching of the configure script

Andreas

ax_boost_thread.m4
Description: application/m4