CMake grammar error

[fuhaixi]

https://github.com/openscenegraph/OpenSceneGraph/blob/2e4ae2ea94595995c1fc56860051410b0c0be605/CMakeModules/OsgMacroUtils.cmake#L176-L182 All "TMPVAR" above is empty. This cause plugins are not built in the plugin folder with Ninja or Makefile. Mabey correct to: FILE(TO_CMAKE_PATH "${CMAKE_ARCHIVE_OUTPUT_DIRECTORY}/${RELATIVE_OUTDIR}" TMPVAR)

[ballastre]

Can confirm, changing to: FILE(TO_CMAKE_PATH "${CMAKE_<...>_OUTPUT_DIRECTORY}/${RELATIVE_OUTDIR}" TMPVAR) puts plugins in the correct directory, and also fixes .pdb installation issues with Ninja, that was "fixed" in #973 workaround.