Find source files.

def source_files(mongodb_path):
    """Find source files."""
    for root, dirs, files in os.walk(mongodb_path):
        for filename in files:
            # skip files in dbtests folder
            if 'dbtests' in root:
                continue
            if filename.endswith(('.cpp', '.c', '.h')):
                yield os.path.join(root, filename)