[physfs] [PATCH] Mark readline.h and history.h as SYSTEM libraries so that GCC ignores warnings for those libs

[Ryan C. Gordon]

> we have applied the attached patch to our clone of PhysFS in order to 
> fix compilation with newer GCC versions. From the CMake docs:

This patch is now 
https://hg.icculus.org/icculus/physfs/rev/4b3c2995ce0f, thanks!

--ryan.