Fix cpplint errors

Fixes errors from the following categories:

- `readability/inheritance`
- `readability/braces`
- `readability/multiline_comment`
- `whitespace/newline`
- `whitespace/empty_if_body`
- `build/include_what_you_use`
- `build/header_guard`

Author: vkucera

ALICE3/Core/ALICE3CoreLinkDef.h

@@ -9,6 +9,8 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
+// NOLINT(build/header_guard)
+
 #pragma link off all globals;
 #pragma link off all classes;
 #pragma link off all functions;

ALICE3/Core/FastTrackerLinkDef.h

@@ -9,8 +9,7 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
-#ifndef ALICE3_CORE_FASTTRACKERLINKDEF_H_
-#define ALICE3_CORE_FASTTRACKERLINKDEF_H_
+// NOLINT(build/header_guard)
 
 #pragma link off all globals;
 #pragma link off all classes;
@@ -19,5 +18,3 @@
 #pragma link C++ class o2::fastsim::GeometryContainer + ;
 #pragma link C++ class o2::fastsim::FastTracker + ;
 #pragma link C++ class o2::fastsim::FlatLutWriter + ;
-
-#endif // ALICE3_CORE_FASTTRACKERLINKDEF_H_