[PERF2BOLT] Fix aggregator wrt new output format of perf

Summary:
Perf is now outputting one less space, which broke our previous
(flaky) assumptions about field separators when processing the output
file. Make it more resilient by accepting any number of spaces before
reading LBR entries.

(cherry picked from FBD6014941)

bolt/DataAggregator.cpp

@@ -476,8 +476,7 @@ ErrorOr<PerfSample> DataAggregator::parseSample() {
   }
 
   while (!checkAndConsumeNewLine()) {
-    if (!expectAndConsumeFS())
-      return make_error_code(llvm::errc::io_error);
+    checkAndConsumeFS();
 
     auto LBRRes = parseLBREntry();
     if (std::error_code EC = LBRRes.getError())