Add clang format & skip build if no source file modified (#5433)

* [BUILD] Add clang format + build skipping

* Add clang-format tool to check codestyle.
Warning: it check the whole modified file, not the diff part, it's why it's lazy. Please also look if rules are perfect, i take the Linux codestyle from LLVM site

Fix issue #5415

* Skip building project if no file is modified
* Fix a wrong brace to trigger LINT

* Make lint step outside of unix build scope

* Add AccessModifierOffset: -8

* Typo fix & needs compile fix

* Fix header priorities

.clang-format

@@ -0,0 +1,12 @@
+BasedOnStyle: LLVM
+IndentWidth: 8
+UseTab: Always
+BreakBeforeBraces: Linux
+AllowShortIfStatementsOnASingleLine: false
+IndentCaseLabels: false
+AccessModifierOffset: -8
+IncludeCategories:
+  - Regex:           '^".*'
+    Priority:        2
+  - Regex:           '^<.*'
+    Priority:        1