Don't force CMAKE_INSTALL_PREFIX on windows (#1478)
Don't force CMAKE_INSTALL_PREFIX on windows (#1478)

Fixes #1477.

Signed-off-by: Steve Peters <19cdd629ec3b4ea4663c77a4169548f370fdc02f@openrobotics.org>
dartsim/dart,dartsim/dart,dartsim/dart,dartsim/dart,dartsim/dart