when compiling with mingw .exe must be added to the binaries
and cmp will find difference in the line endings when running those
binaries under wine, so use diff instead there.

Extend the run_output_test() function so we actually can pass command line
 parameters and so we can support different output files for the same test
 executable.
Also provide some hints about what to do if a test fails (i.e. set VERBOSE=1).