cmake: Only use relative paths for install DESTINATION option (#1405) As described in #1404, the explicit use of CMAKE_INSTALL_PREFIX conflicts with using command-line --prefix. This simply removes all explicit use of CMAKE_INSTALL_PREFIX. Otherwise this path will be duplicated: $ cmake -DCMAKE_BUILD_TYPE=debug -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_INSTALL_PREFIX=inst .. $ DESTDIR=inst ninja install ... -- Installing: inst/src/le/libevent/.cmake-debug/inst/include/event2/util.h -- Installing: inst/src/le/libevent/.cmake-debug/inst/include/event2/ws.h ... Fixes: #1404 Co-authored-by: Jeremy Murphy <jeremymu@blackmagicdesign.com>