Fix UBSAN reported access to withing misaligned addresses

This is can be an issue on ARM, it can cause a hang of
CrashReportTest.MiniDump test on macOS.

src/client/linux/minidump_writer/directory_reader.h

@@ -95,9 +95,10 @@ class DirectoryReader {
 
  private:
   const int fd_;
-  bool hit_eof_;
   unsigned buf_used_;
-  uint8_t buf_[sizeof(struct kernel_dirent) + NAME_MAX + 1];
+  alignas(struct kernel_dirent)
+      uint8_t buf_[sizeof(struct kernel_dirent) + NAME_MAX + 1];
+  bool hit_eof_;
 };
 
 }  // namespace google_breakpad

src/client/linux/minidump_writer/linux_dumper.h

@@ -254,7 +254,7 @@ class LinuxDumper {
   // ID of the crashed thread.
   pid_t crash_thread_;
 
-  mutable PageAllocator allocator_;
+  mutable alignas(MappingInfo) PageAllocator allocator_;
 
   // IDs of all the threads.
   wasteful_vector<pid_t> threads_;