[XRAY] [compiler-rt] [NFC] Fixing the bit twiddling of Function Id in FDR logging mode.

[kpw]

Summary

Fixing a bug I found when testing a reader for the FDR format. Function ID is
now correctly packed into the 28 bits which are documented for it instead of being
masked to all ones.

[dberris]

LGTM

compiler-rt/trunk/lib/xray/xray_fdr_logging.cc

void fdrLoggingHandleArg0(int32_t FuncId,
 
   std::aligned_storage<sizeof(FunctionRecord), alignof(FunctionRecord)>::type
       AlignedFuncRecordBuffer;
   auto &FuncRecord =
       *reinterpret_cast<FunctionRecord *>(&AlignedFuncRecordBuffer);
   FuncRecord.Type = RecordType::Function;
 
   // Only get the lower 28 bits of the function id.
-  FuncRecord.FuncId = FuncId | ~(0x03 << 28);
+  FuncRecord.FuncId = FuncId & ~(0x0F << 28);
 
   // Here we compute the TSC Delta. There are a few interesting situations we
   // need to account for:
   //
   //   - The thread has migrated to a different CPU. If this is the case, then
   //     we write down the following records:
   //
   //       1. A 'NewCPUId' Metadata record.