Try to use readability-identifier-naming check on Clang.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@266184 91177308-0d34-0410-b5e6-96231b3b80d8

.clang-tidy

-Checks: '-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters'
+Checks: '-*,clang-diagnostic-*,llvm-*,misc-*,-misc-unused-parameters,readability-identifier-naming'
+CheckOptions:
+  - key:             readability-identifier-naming.ClassCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.EnumCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.FunctionCase
+    value:           lowerCase
+  - key:             readability-identifier-naming.UnionCase
+    value:           CamelCase
+  - key:             readability-identifier-naming.VariableCase
+    value:           CamelCase