Installer: Converted the build scripts to cmake and added an "installer" target

dist/installer/CMakeLists.txt

@@ -0,0 +1,22 @@
+
+if(WIN32)
+    set(PLATFORM "windows")
+elseif(APPLE)
+    set(PLATFORM "mac")
+elseif(LINUX)
+    set(PLATFORM "linux")
+endif()
+
+set(BUILD_DIR "${CMAKE_BINARY_DIR}/installer")
+set(DIST_DIR "${BUILD_DIR}/dist")
+set(TARGET_FILE "${DIST_DIR}/citra-setup-${PLATFORM}")
+
+# Adds a custom target that will run the BuildInstaller.cmake file
+# CMake can't just run a cmake function as a custom command, so this is a way around it.
+# Calls the cmake command and runs a cmake file in "scripting" mode passing in variables with -D
+add_custom_command(OUTPUT "${TARGET_FILE}"
+    COMMAND ${CMAKE_COMMAND} -DSRC_DIR=${CMAKE_CURRENT_SOURCE_DIR} -D BUILD_DIR=${BUILD_DIR} -D TARGET_FILE=${TARGET_FILE} -P ${CMAKE_SOURCE_DIR}/CMakeModules/BuildInstaller.cmake
+    WORKING_DIRECTORY ${BUILD_DIR}
+)
+
+add_custom_target(installer DEPENDS ${TARGET_FILE})