How to use c99 standard for c files and c++14 with cpp file in a clang front-end tool

I have created a clang front-end tool using libtooling for static analysis. Now I have a source directory which contains both c and cpp files. When I run the tool with this source directory as input, by default for cpp files c++14 standard is used. And for c files there is no mention of standard in clang command. But I want that c99 standard should be used for all the c files. So can we do it in clang front-end tool?

Thanks in advance.

Thanks, Hemant Bhagat