+if 'rbug' not in env['drivers']:
+ env['drivers'].append('rbug')
+if 'galahad' not in env['drivers']:
+ env['drivers'].append('galahad')
+if 'identity' not in env['drivers']:
+ env['drivers'].append('identity')
+if 'softpipe' not in env['drivers']:
+ env['drivers'].append('softpipe')
+if env['llvm'] and 'llvmpipe' not in env['drivers']:
+ env['drivers'].append('llvmpipe')
+if 'sw' not in env['drivers']:
+ env['drivers'].append('sw')