clang-cpp, llvm-g++: add page (#6542)

pages/common/clang-cpp.md

@@ -0,0 +1,7 @@
+# clang-cpp
+
+> This command is an alias of `clang++`.
+
+- View documentation for the original command:
+
+`tldr clang++`

pages/common/llvm-g++.md

@@ -0,0 +1,7 @@
+# llvm-g++
+
+> This command is an alias of `clang++`.
+
+- View documentation for the original command:
+
+`tldr clang++`