From: Gentoo
Subject: Fix tests to use CMAKE_INSTALL_LIBDIR instead of hardcoded lib/

Tests were hardcoding lib/ for library paths, which fails on Gentoo multilib
systems that use lib64/ for 64-bit libraries. Use GNUInstallDirs to detect
the correct library directory.

--- a/test/corrosion_install/install_lib/CMakeLists.txt
+++ b/test/corrosion_install/install_lib/CMakeLists.txt
@@ -1,12 +1,14 @@
 cmake_minimum_required(VERSION 3.15)
 project(test_project VERSION 0.1.0)
 include(ExternalProject)
+include(GNUInstallDirs)
 
 add_library(static_lib STATIC IMPORTED)
 add_library(shared_lib SHARED IMPORTED)
 set(install_prefix "${CMAKE_CURRENT_BINARY_DIR}/rust_lib")
-set(static_lib_install_path "${install_prefix}/lib/${CMAKE_STATIC_LIBRARY_PREFIX}rust_lib${CMAKE_STATIC_LIBRARY_SUFFIX}")
-set(shared_lib_install_path "${install_prefix}/lib/${CMAKE_SHARED_LIBRARY_PREFIX}rust_lib${CMAKE_SHARED_LIBRARY_SUFFIX}")
+# Use CMAKE_INSTALL_LIBDIR to support lib64 on multilib systems
+set(static_lib_install_path "${install_prefix}/${CMAKE_INSTALL_LIBDIR}/${CMAKE_STATIC_LIBRARY_PREFIX}rust_lib${CMAKE_STATIC_LIBRARY_SUFFIX}")
+set(shared_lib_install_path "${install_prefix}/${CMAKE_INSTALL_LIBDIR}/${CMAKE_SHARED_LIBRARY_PREFIX}rust_lib${CMAKE_SHARED_LIBRARY_SUFFIX}")
 
 set_target_properties(static_lib PROPERTIES
                       IMPORTED_LOCATION
@@ -32,7 +34,7 @@ add_custom_target(build_rust_project_dummy
 
 add_dependencies(main-static build_rust_project_dummy)
 
-set(CMAKE_BUILD_RPATH ${install_prefix}/lib)
+set(CMAKE_BUILD_RPATH ${install_prefix}/${CMAKE_INSTALL_LIBDIR})
 add_executable(main-shared main.cpp)
 target_link_libraries(main-shared
         PUBLIC shared_lib)