Fix some warnings on macOS

library/Hooks-darwin.cpp

@@ -314,8 +314,6 @@ DFhackCExport int DFH_SDL_Init(uint32_t flags)
     // prevent any subprocesses from trying to load libdfhack.dylib
     setenv("DYLD_INSERT_LIBRARIES", "", 1);
 
-    DFHack::Core & c = DFHack::Core::getInstance();
-
     int ret = SDL_Init(flags);
     return ret;
 }

library/Hooks-linux.cpp

@@ -139,10 +139,7 @@ DFhackCExport int SDL_Init(uint32_t flags)
         fprintf(stderr,"dfhack: something went horribly wrong\n");
         exit(1);
     }
-    /*
-    DFHack::Core & c = DFHack::Core::getInstance();
-    c.Init();
-    */
+
     int ret = _SDL_Init(flags);
     return ret;
 }

library/Process-darwin.cpp

@@ -50,8 +50,6 @@ using namespace DFHack;
 
 Process::Process(const VersionInfoFactory& known_versions) : identified(false), my_pe(0)
 {
-    int target_result;
-
     char path[1024];
     char *real_path;
     uint32_t size = sizeof(path);