doc: Document that extra-arg/extra-arg-before can be used several times

Hopefully, it will help other people

Author: sylvestre

clang-tools-extra/docs/clang-doc.rst

@@ -81,7 +81,9 @@ Options
 
     --doxygen                   - Use only doxygen-style comments to generate docs.
     --extra-arg=<string>        - Additional argument to append to the compiler command line
+                                  Can be used several times.
     --extra-arg-before=<string> - Additional argument to prepend to the compiler command line
+                                  Can be used several times.
     --format=<value>            - Format for outputted docs.
       =yaml                     -   Documentation in YAML format.
       =md                       -   Documentation in MD format.

clang-tools-extra/docs/clang-rename.rst

@@ -123,7 +123,9 @@ That way you can avoid spelling out all the names as command line arguments:
 
     -export-fixes=<filename>   - YAML file to store suggested fixes in.
     -extra-arg=<string>        - Additional argument to append to the compiler command line
+                                 Can be used several times.
     -extra-arg-before=<string> - Additional argument to prepend to the compiler command line
+                                 Can be used several times.
     -force                     - Ignore nonexistent qualified names.
     -i                         - Overwrite edited <file>s.
     -input=<string>            - YAML file to load oldname-newname pairs from.

clang-tools-extra/docs/clang-tidy/index.rst

@@ -155,7 +155,9 @@ An overview of all the command-line options:
                                      stored fixes can be applied to the input source
                                      code with clang-apply-replacements.
     --extra-arg=<string>           - Additional argument to append to the compiler command line
+                                     Can be used several times.
     --extra-arg-before=<string>    - Additional argument to prepend to the compiler command line
+                                     Can be used several times.
     --fix                          -
                                      Apply suggested fixes. Without -fix-errors
                                      clang-tidy will bail out if any compilation