ffmpeg: pass along CMAKE_OSX_SYSROOT to the linker
Doing so sets the SDK version in the binary, which was previously missing. When the SDK is missing, code verification during loading fails, preventing ParaView from starting.
With this change
> otool -l install/lib/libavformat.dylib | grep sdk
> sdk 10.15.6
Without this change
> otool -l install/lib/libavformat.dylib | grep sdk
> sdk n/a
Fixes #54 (closed).
Edited by Cory Quammen