Builds are not clean between repeated runs

[Andi]

Summary

Motivation:
When doing a compile multiple times in a row only the first build is actually happening.
All subsequent runs to build do nothing as make detects that none of the files have changed.

What changed:
This deletes the entire build directory before each compile happens, thereby ensuring that each run has a clean build.
Since the build directory is deleted before the compile, the "last" build directory is kept. In case there is a failure this build directory can be used to look at what happened.

To delete the build directory I am using the -p flag of runN to perform the cleaning before the timing run.

[cmatthews]

LGTM.

lnt/trunk/lnt/tests/compile.py

 
 def runN(args, N, cwd, preprocess_cmd=None, env=None, sample_mem=False,
          ignore_stderr=False, stdout=None, stderr=None):
     """Interface to runN.
 
     FIXME: Figure out a better way to deal with need to run as root. Maybe farm
     memory sampling process out into something we can setuid? Eek.
     """
+    g_log.info("preprocess_cmd at top of runN: %s:", preprocess_cmd)
     cmd = ['runN', '-a']
     if sample_mem:
         cmd = ['sudo'] + cmd + ['-m']
     if preprocess_cmd is not None:
         cmd.extend(('-p', preprocess_cmd))
     if stdout is not None:
         cmd.extend(('--stdout', stdout))
     if stderr is not None:
elif build_info['style'] == 'make':
         extra_env = config.get('extra_env', {})
         for k in extra_env:
             extra_env[k] = extra_env[k] % env_format
         env.update(extra_env)
 
         # Set build base to copied_src_dir so that if codesize_util
         # is not None, we pass it the correct path.
         build_base = copied_src_dir
+        preprocess_cmd = 'rm -rf "%s"/build' % (build_base,)
+        g_log.info('preprocess_cmd: %s' % preprocess_cmd)
+
     else:
         fatal("unknown build style in project: %r" % project)
 
     # Collect the samples.
     g_log.info('executing full build: %s' % args_to_quoted_string(cmd))
     stdout_path = os.path.join(output_base, "stdout.log")
     stderr_path = os.path.join(output_base, "stderr.log")