This reduces chances of function collision. When using the `fuzz_target` macro, calling `run` inside the block will call the `run` function declared inside the macro definition instead of calling the `run` function defined in the module using `fuzz_target`. Using the `run` function of the macro is probably not the intended goal because it leads to a recursive call. Renaming makes it less likely to call `__libfuzzer_sys_run` by accident.

Rename run to __libfuzzer_sys_run

Fix minor build.rs issues w.r.t. custom libfuzzer paths