[osg] does not build on non windows platforms

[Outurnate]

Host Environment

• OS: Linux 5.4.6-arch3-1 Add libogg/libvorbis/libvorbisfile #1 SMP PREEMPT Tue, 24 Dec 2019 04:36:53 +0000
• Compiler: gcc 9.2.0

To Reproduce
./vcpkg install osg on linux

Failure logs

The following packages will be built and installed:
    osg[core]:x64-linux
Starting package 1/1: osg:x64-linux
Building package osg[core]:x64-linux...
-- Note: osg only supports dynamic library linkage. Building dynamic library.
-- Using cached /var/cache/vcpkg/openscenegraph-OpenSceneGraph-OpenSceneGraph-3.6.4.tar.gz
-- Using source at /usr/share/vcpkg/buildtrees/osg/src/raph-3.6.4-bacad88ef3
-- Configuring x64-linux-dbg
-- Configuring x64-linux-rel
-- Building x64-linux-dbg
CMake Error at scripts/cmake/vcpkg_execute_build_process.cmake:136 (message):
    Command failed: /usr/bin/cmake --build . --config Debug --target install -- -v
    Working Directory: /usr/share/vcpkg/buildtrees/osg/x64-linux-dbg
    See logs for more information:
      /usr/share/vcpkg/buildtrees/osg/install-x64-linux-dbg-out.log

Call Stack (most recent call first):
  scripts/cmake/vcpkg_build_cmake.cmake:91 (vcpkg_execute_build_process)
  scripts/cmake/vcpkg_install_cmake.cmake:24 (vcpkg_build_cmake)
  ports/osg/portfile.cmake:27 (vcpkg_install_cmake)
  scripts/ports.cmake:94 (include)


Error: Building package osg:x64-linux failed with: BUILD_FAILED
Please ensure you're using the latest portfiles with `.\vcpkg update`, then
submit an issue at https://github.com/Microsoft/vcpkg/issues including:
  Package: osg:x64-linux
  Vcpkg version: 2019.09.12-unknownhash

Additionally, attach any relevant sections from the log files above.

Log file install-x64-linux-dbg-out.log

Additional context
OSG_USE_UTF8_FILENAME is defined on all platforms, but it only works on Windows. The symbol causes OSG to use _wfopen instead of fopen. I've fixed this issue with #9441

[JackBoosY]

Hi @Outurnate, thanks for reporting this issue!
I couldn't find any error info in your logs, and osg should be fixed in Linux and OSX.
So please update vcpkg and rebuild it.

Thanks.