KarnstenK sort of gives you the correct answer but it needs expanding
There are two units both trying to define "int8_t" and one of those is part of the standard C library it will be in "StdInt.H" in the system include directory of any C99 compliant compiler.
Fixed width integer types (since C99)
http://en.cppreference.com/w/c/types/integer[
^]
As you are using the standard libraries that you can not get around that unit.
You need to find the none system unit that is also trying to define int8_t and see if you can fix it. There are a number of ways to do that from using #ifndef thru to renaming the non standard unit using of int8_t to a new name.
However to start you need to find what the second unit is that contains the name int8_t because it really shouldn't be defining that particular name and personally I would fix that unit.