src: fix build on certain platforms

The `double` fields in `performance_state` could previously have
been aligned at 4-byte instead of 8-byte boundaries, which would
have made creating an Float64Array them as a array buffer view
for an ArrayBuffer extending over the entire struct an invalid
operation.

Ref: 67269fd

Author: addaleax

src/node_http2.cc

@@ -67,11 +67,12 @@ enum Http2PaddingBufferFields {
 };
 
 struct http2_state {
+  // doubles first so that they are always sizeof(double)-aligned
+  double session_state_buffer[IDX_SESSION_STATE_COUNT];
+  double stream_state_buffer[IDX_STREAM_STATE_COUNT];
   uint32_t padding_buffer[PADDING_BUF_FIELD_COUNT];
   uint32_t options_buffer[IDX_OPTIONS_FLAGS + 1];
   uint32_t settings_buffer[IDX_SETTINGS_COUNT + 1];
-  double session_state_buffer[IDX_SESSION_STATE_COUNT];
-  double stream_state_buffer[IDX_STREAM_STATE_COUNT];
 };
 
 Freelist<nghttp2_data_chunk_t, FREELIST_MAX>

src/node_perf_common.h

@@ -61,8 +61,9 @@ enum PerformanceEntryType {
   } while (0);
 
 struct performance_state {
-  uint32_t observers[NODE_PERFORMANCE_ENTRY_TYPE_INVALID];
+  // doubles first so that they are always sizeof(double)-aligned
   double milestones[NODE_PERFORMANCE_MILESTONE_INVALID];
+  uint32_t observers[NODE_PERFORMANCE_ENTRY_TYPE_INVALID];
 };
 
 }  // namespace performance