API caller: use less collision-prone variable names

In an attempt to declare an API function with a parameter called buffer:

epicardium/api_caller.c: In function 'epic_file_getcwd':
epicardium/api_caller.c:829:14: error: 'buffer' redeclared as different kind of symbol
         void*buffer;
              ^~~~~~
epicardium/api_caller.c:826:28: note: previous definition of 'buffer' was here
 int epic_file_getcwd(char *buffer, size_t bufferSize)

we could really use some sort of "ugly" internal names that are unlikely to be part of a function signature