Fix NULL pointer indirection in FilePath

If the FileBase::lookup operation in the constructor of FilePath returns
NULL, subsequent operations (such as isFile()/isFileSystem()) will call
methods on a NULL 'fb' pointer. This commit fixes this issue by adding
explicit NULL checks and a new method in FilePath (exists()).
Fix GCC interpretation of dependency file

The dependency file generated by GCC might contain more than one
dependency listed on a single line, which wasn't taken into account by the
GCC dependency fille interpreter. This commit fixes this issue.
Merge pull request #54 from ytsuboi/master

Added LPC810 support