I thought we were looking at the function named EZDSP5535_GPIO_init(). This function is apparently not defined in main.c, as I cannot see a definition of this function in main.pp. We would need to look at the .pp file produced from the C file which contains the definition of EZDSP5535_GPIO_init().
If I am correct that CSL_FINS is yet another macro, you will not see it in the .pp file; you will see what it expands to.
I don't know what you mean when you ask how the parsing works. The compiler will preprocess each input file individually to take care of #include and macros, then parse it as C code. This produces object files. Then, the linker combines the object files into an executable program, which you can run. If you need more detail than that, I'll have to refer you to the C Compiler User's Guide.