CMake: Add install target

Do **not** use this with /usr or /usr/local. It creates subdirectories
for resources/translations in the install prefix.

It's intended for creating a relocatable, self-contained bundle, which
can be packaged.

CMakeModules/DuckStationBuildOptions.cmake

@@ -9,6 +9,7 @@ option(BUILD_TESTS "Build unit tests" OFF)
 if(LINUX OR BSD)
   option(ENABLE_X11 "Support X11 window system" ON)
   option(ENABLE_WAYLAND "Support Wayland window system" ON)
+  option(ALLOW_INSTALL "Allow installation to CMAKE_INSTALL_PREFIX" OFF)
 endif()
 if(APPLE)
   option(SKIP_POSTPROCESS_BUNDLE "Disable bundle post-processing, including Qt additions" OFF)

CMakeModules/DuckStationBuildSummary.cmake

@@ -24,6 +24,12 @@ if(BUILD_TESTS)
   message(STATUS "Building unit tests.")
 endif()
 
+if(ALLOW_INSTALL)
+  message(WARNING "Install target is enabled. This will install all DuckStation files into:
+  ${CMAKE_INSTALL_PREFIX}
+It does **not** use the LSB subdirectories of bin, share, etc, so you should disable this option if it is set to /usr or /usr/local.")
+endif()
+
 if(NOT IS_SUPPORTED_COMPILER)
   message(WARNING "
 *************** UNSUPPORTED CONFIGURATION ***************

CMakeModules/DuckStationUtils.cmake

@@ -221,3 +221,9 @@ function(get_scm_version)
     set(SCM_VERSION ${LOCAL_SCM_VERSION} PARENT_SCOPE)
   endif()
 endfunction()
+
+function(install_imported_dep_library name)
+  get_target_property(SONAME "${name}" IMPORTED_SONAME_RELEASE)
+  get_target_property(LOCATION "${name}" IMPORTED_LOCATION_RELEASE)
+  install(FILES "${LOCATION}" RENAME "${SONAME}" DESTINATION "${CMAKE_INSTALL_PREFIX}")
+endfunction()