make tests run when compiling with mingw for windows

Hello,

This commit makes the tests run under wine when compiling with mingw.
There are two issues, one is that .exe must be added for the binaries in test-defs.sh, the second is that running under wine adds \r to the output which cmp will fail on so this uses diff -w instead.

I tested this on a ubuntu 12.10 x64 with mingw64 installed running:
```
ac_cv_func_realloc_0_nonnull=yes ac_cv_func_malloc_0_nonnull=yes ./configure ./configure --host=x86_64-w64-mingw32  --build=x86_64-unknown-linux-gnu  && USE_VALGRIND=0 make check
```

/klas