Core: Fix compiling on Fedora (G3D related)

Thanks F3st and Gamera

Closes #7477

dep/g3dlite/G3D-v8.0_extra.diff

@@ -0,0 +1,12 @@
+diff --git a/dep/g3dlite/include/G3D/GMutex.h b/dep/g3dlite/include/G3D/GMutex.h
+index 3469b81..9fe098d 100644
+--- a/dep/g3dlite/include/G3D/GMutex.h
++++ b/dep/g3dlite/include/G3D/GMutex.h
+@@ -16,6 +16,7 @@
+ #ifndef G3D_WIN32
+ #   include <pthread.h>
+ #   include <signal.h>
++#   include <unistd.h>
+ #endif
+ 
+ 

dep/g3dlite/include/G3D/GMutex.h

@@ -16,6 +16,7 @@
 #ifndef G3D_WIN32
 #   include <pthread.h>
 #   include <signal.h>
+#   include <unistd.h>
 #endif