I am learning compilers and want to make changes of my own to GCC parser and lexer. Is there any testing tool or some another way available which let me change gcc code and test it accordingly.
I tried changing the lexical analysis file but now I am stuck because I don't know how to compile these files. I tried the compilation using other GCC compiler but show errors. I even tried configure and make but doing this with every change does not seems efficient.
The purpose of these changes is just learning and I have to consider GCC only as this is the only compiler my instructor allowed.
I even tried configure and make but doing that wit every change is not at all efficient.
That is exactly what you should be doing. (Well, you don't need to re-configure after every change, just run make again.) However, by default GCC configures itself in bootstrap mode, which means not only does your host compiler compile GCC, that compiled GCC then compiles GCC again (and again). That is overkill for your purposes, and you can prevent that from happening by adding --disable-bootstrap to the configuration options.
Another option that can help significantly reduce build times is enabling only the languages you're interested in. Since you're experimenting, you'll likely be very happy if you create something that works for C or for C++, even if for some obscure reason Java happens to break. Testing other languages becomes relevant when you make your changes available for a larger audience, but that isn't the case just yet. The configuration option that covers this is --enable-languages=c,c++.
Most of the configuration options are documented on the Installing GCC: Configuration page. Throroughly testing your changes is documented on the Contributing to GCC page, but that's likely something for later: you should know how to make your own simpler tests pass, by simply trying code that makes use of your new feature.