Fix LLDB build on old Linux kernels (pre-4.1)

These fields are guarded elsewhere, but were missing here.

Reviewed By: wallace

Differential Revision: https://reviews.llvm.org/D133778

Author: DavidSpickett

lldb/source/Plugins/Process/Linux/Perf.cpp

@@ -125,6 +125,10 @@ llvm::Error PerfEvent::MmapMetadataAndDataBuffer(size_t num_data_pages,
 }
 
 llvm::Error PerfEvent::MmapAuxBuffer(size_t num_aux_pages) {
+#ifndef PERF_ATTR_SIZE_VER5
+  return createStringError(inconvertibleErrorCode(),
+                           "Intel PT Linux perf event not supported");
+#else
   if (num_aux_pages == 0)
     return Error::success();
 
@@ -141,6 +145,7 @@ llvm::Error PerfEvent::MmapAuxBuffer(size_t num_aux_pages) {
     return Error::success();
   } else
     return mmap_aux.takeError();
+#endif
 }
 
 llvm::Error PerfEvent::MmapMetadataAndBuffers(size_t num_data_pages,
@@ -170,16 +175,24 @@ perf_event_mmap_page &PerfEvent::GetMetadataPage() const {
 }
 
 ArrayRef<uint8_t> PerfEvent::GetDataBuffer() const {
+#ifndef PERF_ATTR_SIZE_VER5
+  llvm_unreachable("Intel PT Linux perf event not supported");
+#else
   perf_event_mmap_page &mmap_metadata = GetMetadataPage();
   return {reinterpret_cast<uint8_t *>(m_metadata_data_base.get()) +
               mmap_metadata.data_offset,
           static_cast<size_t>(mmap_metadata.data_size)};
+#endif
 }
 
 ArrayRef<uint8_t> PerfEvent::GetAuxBuffer() const {
+#ifndef PERF_ATTR_SIZE_VER5
+  llvm_unreachable("Intel PT Linux perf event not supported");
+#else
   perf_event_mmap_page &mmap_metadata = GetMetadataPage();
   return {reinterpret_cast<uint8_t *>(m_aux_base.get()),
           static_cast<size_t>(mmap_metadata.aux_size)};
+#endif
 }
 
 Expected<std::vector<uint8_t>> PerfEvent::GetReadOnlyDataBuffer() {
@@ -188,6 +201,10 @@ Expected<std::vector<uint8_t>> PerfEvent::GetReadOnlyDataBuffer() {
   // this piece of code updates some pointers. See more about data_tail
   // in https://man7.org/linux/man-pages/man2/perf_event_open.2.html.
 
+#ifndef PERF_ATTR_SIZE_VER5
+  return createStringError(inconvertibleErrorCode(),
+                           "Intel PT Linux perf event not supported");
+#else
   bool was_enabled = m_enabled;
   if (Error err = DisableWithIoctl())
     return std::move(err);
@@ -224,6 +241,7 @@ Expected<std::vector<uint8_t>> PerfEvent::GetReadOnlyDataBuffer() {
   }
 
   return output;
+#endif
 }
 
 Expected<std::vector<uint8_t>> PerfEvent::GetReadOnlyAuxBuffer() {
@@ -232,6 +250,10 @@ Expected<std::vector<uint8_t>> PerfEvent::GetReadOnlyAuxBuffer() {
   // this piece of code updates some pointers. See more about aux_tail
   // in https://man7.org/linux/man-pages/man2/perf_event_open.2.html.
 
+#ifndef PERF_ATTR_SIZE_VER5
+  return createStringError(inconvertibleErrorCode(),
+                           "Intel PT Linux perf event not supported");
+#else
   bool was_enabled = m_enabled;
   if (Error err = DisableWithIoctl())
     return std::move(err);
@@ -264,6 +286,7 @@ Expected<std::vector<uint8_t>> PerfEvent::GetReadOnlyAuxBuffer() {
   }
 
   return output;
+#endif
 }
 
 Error PerfEvent::DisableWithIoctl() {
@@ -295,11 +318,15 @@ Error PerfEvent::EnableWithIoctl() {
 }
 
 size_t PerfEvent::GetEffectiveDataBufferSize() const {
+#ifndef PERF_ATTR_SIZE_VER5
+  llvm_unreachable("Intel PT Linux perf event not supported");
+#else
   perf_event_mmap_page &mmap_metadata = GetMetadataPage();
   if (mmap_metadata.data_head < mmap_metadata.data_size)
     return mmap_metadata.data_head;
   else
     return mmap_metadata.data_size; // The buffer has wrapped.
+#endif
 }
 
 Expected<PerfEvent>