[lld][benchmark] Make path to LLD configurable

[int3]

Summary

And record it in the Run Info so we can distinguish LLD-ELF vs
LLD-MachO runs on LNT.

[compnerd]

Seems like this just adds an option to control a hardcoded value, which is reasonable.

lld/utils/benchmark.py

 except ImportError:
     from urllib import urlencode
     from urllib2 import urlopen, Request
 
 
 parser = argparse.ArgumentParser()
 parser.add_argument('benchmark_directory')
 parser.add_argument('--runs', type=int, default=10)
+parser.add_argument('--lld', help='Path to the lld binary', default='../ld.lld')
 parser.add_argument('--wrapper', default='')
 parser.add_argument('--machine', required=True)
 parser.add_argument('--revision', required=True)
 parser.add_argument('--threads', action='store_true')
 parser.add_argument('--url', help='The lnt server url to send the results to',
                     default='http://localhost:8000/db_default/v4/link/submitRun')
 args = parser.parse_args()
 
def perf(cmd):
     os.unlink('t')
     return ret
 
 def runBench(bench):
     thread_arg = [] if args.threads else ['--no-threads']
     os.chdir(bench.directory)
     suffix = '-%s' % bench.variant if bench.variant else ''
     response = 'response' + suffix + '.txt'
-    ret = perf(['../ld.lld', '@' + response, '-o', 't'] + thread_arg)
+    ret = perf([args.lld, '@' + response, '-o', 't'] + thread_arg)
     ret['name'] = str(bench)
     os.chdir('..')
     return ret
 
 def buildLntJson(benchmarks):
     start = datetime.datetime.utcnow().isoformat()
     tests = [runBench(b) for b in benchmarks]
     end = datetime.datetime.utcnow().isoformat()
     ret = {
         'format_version' : '2',
         'machine' : { 'name' : args.machine },
         'run' : {
+            'lld_name': os.path.basename(args.lld),
             'end_time' : start,
             'start_time' : end,
             'llvm_project_revision': args.revision
         },
         'tests' : tests
     }
     return json.dumps(ret, sort_keys=True, indent=4)
 
 def submitToServer(data):
     data2 = urlencode({ 'input_data' : data }).encode('ascii')
     urlopen(Request(args.url, data2))
 
 os.chdir(args.benchmark_directory)
 data = buildLntJson(getBenchmarks())
 submitToServer(data)