make / cortex m: replace hyphen in module name

When you compile for UDOO, you are greeted by a multitude of this
warnings:
```
<command-line>:0:14: warning: ISO C99 requires whitespace after the macro name [enabled by default]
```

The reason for that is the argument `-DMODULE_CORTEX-M3_COMMON`.

This PR fixes this problem by replacing hyphens with underscores for the
`-D…` argument.