Fix cross compiling on OS X.

- The OS X specific flags must not be set when cross compiling. Check for a
  MinGW compiler on OS X before adding them.
- Do not set CC explicitly in chinachippatcher, it will be set from Rockbox
  Utility's Makefile.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@31527 a1c6a512-1295-4272-9138-f99709370657
2 files changed