[physfs] Cross compiling PhysicsFS 3.0.1 using MinGW on Linux

[Ryan C. Gordon]

> set(CMAKE_SYSTEM_NAME Windows)

This is the magic that should avoid adding -rdynamic (it picks that up 
from the Modules/Platform/Linux-GNU.cmake file, wherever CMake is 
installed, and CMAKE_SYSTEM_NAME should tell it not to even look at that 
file).

My _guess_ is that you have -rdynamic cached from a previous build 
attempt before you wrote the toolchain file. If I'm right (this is 
arguably a CMake bug, but), delete your build directory completely and 
let it start from scratch with your toolchain file, and see if that 
resolves it.

--ryan.