build: add build script to configure kernel and tools build systems

arch/x86_64/config.cmake

@@ -3,3 +3,8 @@ target_compile_options(${kernel_exe_name} PRIVATE
 	-mno-sse -mno-sse2 -D_64BIT -DBYTE_ORDER=1234)
 target_link_libraries(${kernel_exe_name} "-z max-page-size=0x1000" "-T ${CMAKE_CURRENT_SOURCE_DIR}/arch/x86_64/layout.ld")
 
+add_custom_command(TARGET ${kernel_exe_name} POST_BUILD
+	COMMAND ${BUILD_TOOLS_DIR}/e64patch $<TARGET_FILE:${kernel_exe_name}>
+	WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
+	COMMENT "Patching kernel elf64 image"
+)

arch/x86_64/toolchain.cmake

@@ -1,5 +1,5 @@
 # the name of the target operating system
-set(CMAKE_SYSTEM_NAME Magenta)
+set(CMAKE_SYSTEM_NAME Mango)
 
 # which compilers to use for C and C++
 set(CMAKE_C_COMPILER   x86_64-elf-gcc)