[cmake] Fix libneko.so loading error when installing to /usr/local (#271)

* [cmake] Add install library path to rpath

This way rpath is correctly set by default, avoiding errors like:
`libneko.so.2: cannot open shared object file` when installing to
/usr/local/

* [cmake] Don't set LD_LIBRARY_PATH during tests

If rpath is set correctly then this is not necessary

* [cmake] Clean up rpath settings

Only build with install path if RELOCATABLE is on, otherwise we can stick to
the default build rpath.

We were setting these options to their default values:
CMAKE_MACOS_RPATH, CMAKE_SKIP_BUILD_RPATH, CMAKE_SKIP_INSTALL_RPATH

Author: tobil4sk

CMakeLists.txt

@@ -158,23 +158,19 @@ endforeach()
 
 include(ExternalProject)
 
-
-# CMAKE_BUILD_WITH_INSTALL_RPATH should be set to true.
-# It is because `nekotools boot` will use the neko in build dir during build.
-set(CMAKE_BUILD_WITH_INSTALL_RPATH TRUE)
-
 if (RELOCATABLE)
-	# https://cmake.org/Wiki/CMake_RPATH_handling
-	set(CMAKE_SKIP_BUILD_RPATH FALSE)
-	set(CMAKE_SKIP_INSTALL_RPATH FALSE)
+	# https://gitlab.kitware.com/cmake/community/-/wikis/doc/cmake/RPATH-handling
+	# Set this to true, otherwise the binaries won't be relocatable until after installation:
+	set(CMAKE_BUILD_WITH_INSTALL_RPATH TRUE)
 	if(APPLE)
-		set(CMAKE_MACOSX_RPATH TRUE)
 		set(CMAKE_INSTALL_RPATH @executable_path/)
 	elseif(UNIX)
 		set(CMAKE_INSTALL_RPATH \$ORIGIN)
 	endif()
 endif()
 
+list(APPEND CMAKE_INSTALL_RPATH ${CMAKE_INSTALL_FULL_LIBDIR})
+
 if(UNIX AND NOT APPLE)
 	add_definitions(-DABI_ELF)
 endif()
@@ -395,12 +391,9 @@ set_target_properties(libneko
 if (CMAKE_HOST_WIN32)
 	set(set_neko_env set NEKOPATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY})
 	set(neko_exec $<TARGET_FILE:nekovm>)
-elseif(CMAKE_HOST_APPLE)
-	set(set_neko_env "")
-	set(neko_exec DYLD_FALLBACK_LIBRARY_PATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY} NEKOPATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY} $<TARGET_FILE:nekovm>)
 else()
 	set(set_neko_env "")
-	set(neko_exec LD_LIBRARY_PATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY} NEKOPATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY} $<TARGET_FILE:nekovm>)
+	set(neko_exec NEKOPATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY} $<TARGET_FILE:nekovm>)
 endif()
 
 file(GLOB compilers_src
@@ -781,26 +774,13 @@ if (WITH_NEKOML)
 		COMMAND nekoml
 		WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}
 	)
-
-	set_tests_properties(nekoml
-		PROPERTIES
-		ENVIRONMENT LD_LIBRARY_PATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY}
-	)
 endif()
 
 add_test(NAME nekotools
 	COMMAND nekotools
 	WORKING_DIRECTORY ${CMAKE_RUNTIME_OUTPUT_DIRECTORY}
 )
 
-if (UNIX AND NOT APPLE)
-	set_tests_properties(-version test.n nekoc nekotools
-		PROPERTIES
-		ENVIRONMENT LD_LIBRARY_PATH=${CMAKE_RUNTIME_OUTPUT_DIRECTORY}
-	)
-endif()
-
-
 #######################
 
 # debian source packages