Previously, the clean target would delete a number of file extensions, many of which currently unknown to our build system (old platforms?). This commit changes the target so that it only cleans what we know we are building. Platforms / CPUs can append to the target with platform-specific build artifacts.
The rule is changed such that it makes sure the .map file gets built first. We have separate map files per project, so we need separate mspsim-maptables
