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

PWGEM/Dilepton/Core/PWGEMDileptonCoreLinkDef.h

@@ -9,8 +9,7 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
-#ifndef PWGEM_DILEPTON_CORE_PWGEMDILEPTONCORELINKDEF_H_
-#define PWGEM_DILEPTON_CORE_PWGEMDILEPTONCORELINKDEF_H_
+// NOLINT(build/header_guard)
 
 #pragma link off all globals;
 #pragma link off all classes;
@@ -20,5 +19,3 @@
 #pragma link C++ class DielectronCut + ;
 #pragma link C++ class DimuonCut + ;
 #pragma link C++ class EMTrackCut + ;
-
-#endif // PWGEM_DILEPTON_CORE_PWGEMDILEPTONCORELINKDEF_H_

PWGEM/Dilepton/DataModel/EvSelFlags.h

@@ -9,8 +9,8 @@
 // granted to it by virtue of its status as an Intergovernmental Organization
 // or submit itself to any jurisdiction.
 
-#ifndef PWGEM_DILEPTON_CORE_EVSELFLAGS_H
-#define PWGEM_DILEPTON_CORE_EVSELFLAGS_H
+#ifndef PWGEM_DILEPTON_DATAMODEL_EVSELFLAGS_H_
+#define PWGEM_DILEPTON_DATAMODEL_EVSELFLAGS_H_
 
 namespace o2::aod::emevsel
 {
@@ -37,4 +37,4 @@ enum EventSelectionFlags {
 };
 } // namespace o2::aod::emevsel
 
-#endif // PWGEM_DILEPTON_CORE_EVSELFLAGS_H
+#endif // PWGEM_DILEPTON_DATAMODEL_EVSELFLAGS_H_

PWGEM/Tasks/phosCalibration.cxx

@@ -44,6 +44,7 @@
 #include <cstdint>
 #include <cstdlib>
 #include <memory>
+#include <string>
 #include <vector>
 
 using namespace o2;